Slideshow: Brussels attacks

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The blown out windows of Zaventem airport are seen after a deadly attack in Brussels, Belgium, Tuesday, March 22, 2016. Authorities in Europe have tightened security at airports, on subways, at the borders and on city streets after deadly attacks Tuesday on the Brussels airport and its subway system. (AP Photo/Peter Dejong)

by: Associated Press

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Belgian Prime Minister Charles Michel, left, and Belgium's Interior Minister Jan Jambon prepare to address a media conference in Brussels on Tuesday, March 22, 2016. Explosions, at least one likely caused by a suicide bomber, rocked the Brussels airport and subway system Tuesday, prompting a lockdown of the Belgian capital and heightened security across Europe. (AP Photo/Geert Vanden Wijngaert)

by: Associated Press

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Police stand outside a metro station after an explosion in Brussels on Tuesday, March 22, 2016. Explosions, at least one likely caused by a suicide bomber, rocked the Brussels airport and subway system Tuesday, prompting a lockdown of the Belgian capital and heightened security across Europe. (AP Photo/Geert Vanden Wijngaert)

by: Associated Press

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The blown out facade of the terminal is seen as an ambulance leaves Zaventem airport, one of the sites of two deadly attacks in Brussels, Belgium, Tuesday, March 22, 2016. Authorities in Europe have tightened security at airports, on subways, at the borders and on city streets after the attacks Tuesday on the Brussels airport and its subway system. (AP Photo/Peter Dejong)

by: Associated Press

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Police stand outside a metro station after an explosion in Brussels on Tuesday, March 22, 2016. Explosions, at least one likely caused by a suicide bomber, rocked the Brussels airport and subway system Tuesday, prompting a lockdown of the Belgian capital and heightened security across Europe. (AP Photo/Geert Vanden Wijngaert)

by: Associated Press

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People react outside Brussels airport after explosions rocked the facility in Brussels, Belgium Tuesday March 22, 2016. Explosions rocked the Brussels airport and the subway system Tuesday, just days after the main suspect in the November Paris attacks was arrested in the city, police said. (AP Photo/Geert Vanden Wijngaert)

by: Associated Press

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An Israeli airport security guard patrols with a dog in Ben Gurion airport near Tel Aviv, Israel, Tuesday, March 22, 2016. After the Brussels attacks, Israel briefly announced that all Israeli flights from Europe were canceled, then reinstated the flights, Israel Airports Authority spokesman Ofer Leffler said. Pini Schiff, former director of security at Ben-Gurion Airport, said the attack in the Brussels airport was “a colossal failure” of Belgian security, and he said “the chances are very low” that such a bombing could take place in Israel’s airport. Israel's Ben-Gurion Airport is considered among the most secure in the world, an outcome stemming from several Palestinian attacks on Israeli planes and travelers in the 1970s. (AP Photo/Ariel Schalit)

by: Associated Press

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An injured man gestures outsude Brussels airport after explosions rocked the facility in Brussels, Belgium Tuesday March 22, 2016. Explosions rocked the Brussels airport and the subway system Tuesday, just days after the main suspect in the November Paris attacks was arrested in the city, police said. (AP Photo/Geert Vanden Wijngaert)

by: Associated Press

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People react as they walk away from Brussels airport after explosions rocked the facility in Brussels, Belgium Tuesday March 22, 2016. Explosions rocked the Brussels airport and the subway system Tuesday, just days after the main suspect in the November Paris attacks was arrested in the city, police said. (AP Photo/Geert Vanden Wijngaert)

by: Associated Press

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People are evacuated from Brussels airport after explosions rocked the facility in Brussels, Belgium Tuesday March 22, 2016. Explosions rocked the Brussels airport and the subway system Tuesday, just days after the main suspect in the November Paris attacks was arrested in the city, police said. (AP Photo/Geert Vanden Wijngaert)

by: Associated Press

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People stand near Brussels airport after being evacuated following explosions that rocked the facility in Brussels, Belgium, Tuesday March 22, 2016. Authorities locked down the Belgian capital on Tuesday after explosions rocked the Brussels airport and subway system, killing a number of people and injuring many more. Belgium raised its terror alert to its highest level, diverting arriving planes and trains and ordering people to stay where they were. Airports across Europe tightened security. (AP Photo/Geert Vanden Wijngaert)

by: Associated Press

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People walk away from Brussels airport after explosions rocked the facility in Brussels, Belgium Tuesday March 22, 2016. Explosions rocked the Brussels airport and the subway system Tuesday, just days after the main suspect in the November Paris attacks was arrested in the city, police said. (AP Photo/Geert Vanden Wijngaert)

by: Associated Press

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The blown out facade of the terminal is seen, center, at Zaventem airport, one of the sites of two deadly attacks in Brussels, Belgium, Tuesday, March 22, 2016. Authorities in Europe have tightened security at airports, on subways, at the borders and on city streets after the attacks Tuesday on the Brussels airport and its subway system. (AP Photo/Peter Dejong)

by: Associated Press

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U.S. Capitol Police officers stand guard outside at the entrance to the House of Representatives on Capitol Hill in Washington, Tuesday, March 22, 2016. Deadly explosions ripped through the Brussels airport and a subway station Tuesday during the morning rush hour, only days after the prime suspect in the Paris terror attacks Salah Abdeslam was arrested in Brussels. (AP Photo/J. Scott Applewhite)

by: Associated Press

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The Eiffel Tower is illuminated with the Belgium national colors black, yellow and red in honor of the victims of the today's attacks at the airport and the metro station in Brussels, in Paris, Tuesday, March 22, 2016. Explosions, at least one likely caused by a suicide bomber, rocked the Brussels airport and its subway system Tuesday, prompting a lockdown of the Belgian capital and heightened security across Europe. (AP Photo/Thibault Camus)

by: Associated Press

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Police patrol the EU commission building, after a bomb exploded nearby, at the subway in Brussels, Belgium, Tuesday, March 22, 2016. Authorities locked down the Belgian capital on Tuesday after explosions rocked the Brussels airport and subway system, killing a number of people and injuring many more. Belgium raised its terror alert to its highest level, diverting arriving planes and trains and ordering people to stay where they were. Airports across Europe tightened security. (AP Photo/Martin Meissner)

by: Associated Press

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A writing on the asphalt reads "Brussels forever" at the place de la Bourse in the center of Brussels, where people write hundreds of messages on the ground to remember the victims of todays attack, Tuesday, March 22, 2016. Bombs exploded at the Brussels airport and one of the city's metro stations Tuesday, killing and wounding scores of people, as a European capital was again locked down amid heightened security threats. (AP Photo/Martin Meissner)

by: Associated Press

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Two Belgian flags are projected on Rome's Campidoglio Capitol Hill to honor the victims of the deadly attacks at Brussels airport and subway, Tuesday, March 22, 2016. Explosions, at least one likely caused by a suicide bomber, rocked the Brussels airport and its subway system prompting a lockdown of the Belgian capital and heightened security across Europe. (AP Photo/Andrew Medichini)

by: Associated Press

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The Brandenburg Gate is illuminated with the Belgium national flag in reaction to the Brussels attacks, in Berlin, Germany, Tuesday, March 22, 2016. (AP Photo/Markus Schreiber)

by: Associated Press

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Solidarity messages are written in chalk outside the stock exchange in Brussels on Tuesday, March 22, 2016. Explosions, at least one likely caused by a suicide bomber, rocked the Brussels airport and subway system Tuesday, prompting a lockdown of the Belgian capital and heightened security across Europe. At least 26 people were reported dead. (AP Photo/Geert Vanden Wijngaert)

by: Associated Press

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The Brandenburg Gate is illuminated with the Belgian national flag in reaction to the Brussels attacks, in Berlin, Germany, Tuesday, March 22, 2016. (AP Photo/Markus Schreiber)

by: Associated Press

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A memorial to attack victims with a Belgian flag and flowers is set up outside the stock exchange in Brussels on Tuesday, March 22, 2016. Explosions, at least one likely caused by a suicide bomber, rocked the Brussels airport and subway system Tuesday, prompting a lockdown of the Belgian capital and heightened security across Europe. (AP Photo/Geert Vanden Wijngaert)

by: Associated Press

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People bring flowers and candles to mourn for the victims at Place de la Bourse in the center of Brussels, Tuesday, March 22, 2016. Bombs exploded at the Brussels airport and one of the city's metro stations Tuesday, killing and wounding scores of people, as a European capital was again locked down amid heightened security threats. (AP Photo/Martin Meissner)

by: Associated Press

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Travelers wait at the counter of Brussels airlines in Ben Gurion airport near Tel Aviv, Israel, Tuesday, March 22, 2016. After the Brussels attacks, Israel briefly announced that all Israeli flights from Europe were canceled, then reinstated the flights, Israel Airports Authority spokesman Ofer Leffler said. Pini Schiff, former director of security at Ben-Gurion Airport, said the attack in the Brussels airport was “a colossal failure” of Belgian security, and he said “the chances are very low” that such a bombing could take place in Israel’s airport. Israel's Ben-Gurion Airport is considered among the most secure in the world, an outcome stemming from several Palestinian attacks on Israeli planes and travelers in the 1970s. (AP Photo/Ariel Schalit)

by: Associated Press

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People mourn for the victims at Place de la Bourse in the center of Brussels, Tuesday, March 22, 2016. Bombs exploded at the Brussels airport and one of the city's metro stations Tuesday, killing and wounding scores of people, as a European capital was again locked down amid heightened security threats. (AP Photo/Martin Meissner)

by: Associated Press

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People comfort each other after being evacuated from Brussels airport, after explosions rocked the facility in Brussels, Belgium, Tuesday March 22, 2016. Authorities locked down the Belgian capital on Tuesday after explosions rocked the Brussels airport and subway system, killing at least 13 people and injuring many more. Belgium raised its terror alert to its highest level, diverting arriving planes and trains and ordering people to stay where they were. Airports across Europe tightened security. (AP Photo/Geert Vanden Wijngaert)

by: Associated Press

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People bring flowers and candles to mourn for the victims at Place de la Bourse in the center of Brussels, Tuesday, March 22, 2016. Bombs exploded at the Brussels airport and one of the city's metro stations Tuesday, killing and wounding scores of people, as a European capital was again locked down amid heightened security threats. (AP Photo/Martin Meissner)

by: Associated Press

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People put the Brussel's mascot statue with a Belgian flag to mourn for the victims at Place de la Bourse in the center of Brussels, Tuesday, March 22, 2016. Bombs exploded at the Brussels airport and one of the city's metro stations Tuesday, killing and wounding scores of people, as a European capital was again locked down amid heightened security threats. (AP Photo/Martin Meissner)

by: Associated Press

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Ambulances arrive to the scene at Brussels airport, after explosions rocked the facility in Brussels, Belgium, Tuesday March 22, 2016. Authorities locked down the Belgian capital on Tuesday after explosions rocked the Brussels airport and subway system, killing at least 13 people and injuring many more. Belgium raised its terror alert to its highest level, diverting arriving planes and trains and ordering people to stay where they were. Airports across Europe tightened security. (AP Photo/Geert Vanden Wijngaert)

by: Associated Press

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Police and rescue teams are pictured outside the metro station Maelbeek in Brussels, Tuesday, March 22, 2016. Explosions, at least one likely caused by a suicide bomber, rocked the Brussels airport and its subway system Tuesday, prompting a lockdown of the Belgian capital and heightened security across Europe. (AP Photo/Martin Meissner)

by: Associated Press

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People stand near Brussels airport after being evacuated following explosions that rocked the facility in Brussels, Belgium, Tuesday March 22, 2016. Authorities locked down the Belgian capital on Tuesday after explosions rocked the Brussels airport and subway system, killing a number of people and injuring many more. Belgium raised its terror alert to its highest level, diverting arriving planes and trains and ordering people to stay where they were. Airports across Europe tightened security. (AP Photo/Geert Vanden Wijngaert)

by: Associated Press

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A man looks at flowers and messages outside the stock exchange in Brussels on Tuesday, March 22, 2016. Explosions, at least one likely caused by a suicide bomber, rocked the Brussels airport and subway system Tuesday, prompting a lockdown of the Belgian capital and heightened security across Europe. At least 26 people were reported dead. (AP Photo/Geert Vanden Wijngaert)

by: Associated Press

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One World Trade Center is shown Tuesday, March 22, 2016, in New York. New York Gov. Andrew Cuomo has directed One World Trade Center be displayed in the Belgium colors of black, yellow and red to show solidarity with the nation following attacks that killed dozens of people in Brussels. (AP Photo/Frank Franklin II)

by: Associated Press

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An Israeli airport security guard patrols with a dog in Ben Gurion airport near Tel Aviv, Israel, Tuesday, March 22, 2016. After the Brussels attacks, Israel briefly announced that all Israeli flights from Europe were canceled, then reinstated the flights, Israel Airports Authority spokesman Ofer Leffler said. Pini Schiff, former director of security at Ben-Gurion Airport, said the attack in the Brussels airport was “a colossal failure” of Belgian security, and he said “the chances are very low” that such a bombing could take place in Israel’s airport. Israel's Ben-Gurion Airport is considered among the most secure in the world, an outcome stemming from several Palestinian attacks on Israeli planes and travelers in the 1970s. (AP Photo/Ariel Schalit)

by: Associated Press

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People walk away from Brussels airport after explosions rocked the facility in Brussels, Belgium Tuesday March 22, 2016. Explosions rocked the Brussels airport and the subway system Tuesday, just days after the main suspect in the November Paris attacks was arrested in the city, police said. (AP Photo/Geert Vanden Wijngaert)

by: Associated Press

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People walk away from the broken windows at Zaventem Airport in Brussels after an explosion on Tuesday, March 22, 2016. Explosions, at least one likely caused by a suicide bomber, rocked the Brussels airport and subway system Tuesday, prompting a lockdown of the Belgian capital and heightened security across Europe. At least 26 people were reported dead. (AP Photo/Geert Vanden Wijngaert)

by: Associated Press

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People stand near Brussels airport after being evacuated following explosions that rocked the facility in Brussels, Belgium, Tuesday March 22, 2016. Authorities locked down the Belgian capital on Tuesday after explosions rocked the Brussels airport and subway system, killing a number of people and injuring many more. Belgium raised its terror alert to its highest level, diverting arriving planes and trains and ordering people to stay where they were. Airports across Europe tightened security. (AP Photo/Geert Vanden Wijngaert)

by: Associated Press

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An Israeli airport security guard patrols with a dog in Ben Gurion airport near Tel Aviv, Israel, Tuesday, March 22, 2016. After the Brussels attacks, Israel briefly announced that all Israeli flights from Europe were canceled, then reinstated the flights, Israel Airports Authority spokesman Ofer Leffler said. Pini Schiff, former director of security at Ben-Gurion Airport, said the attack in the Brussels airport was “a colossal failure” of Belgian security, and he said “the chances are very low” that such a bombing could take place in Israel’s airport. Israel's Ben-Gurion Airport is considered among the most secure in the world, an outcome stemming from several Palestinian attacks on Israeli planes and travelers in the 1970s. (AP Photo/Ariel Schalit)

by: Associated Press

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A woman is evacuated in an ambulance by emergency services after a explosion in a main metro station in Brussels on Tuesday, March 22, 2016. Explosions rocked the Brussels airport and the subway system Tuesday, killing at least 13 people and injuring many others just days after the main suspect in the November Paris attacks was arrested in the city, police said. (AP Photo/Virginia Mayo)

by: Associated Press

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Smoke billows from the Zaventem Airport after a controlled explosion in Brussels, Tuesday, March 22, 2016. Bombs struck the Brussels airport and one of the city's metro stations Tuesday, killing and wounding dozens of people, as a European capital was again locked down amid heightened security threats. (AP Photo/Michel Spingler)

by: Associated Press

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The blown out windows of Zaventem airport are seen after a deadly attack in Brussels, Belgium, Tuesday, March 22, 2016. Authorities in Europe have tightened security at airports, on subways, at the borders and on city streets after deadly attacks Tuesday on the Brussels airport and its subway system. (AP Photo/Peter Dejong)

by: Associated Press

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Writing on the asphalt reads "More stars in Brussel's heaven" at Place de la Bourse in the center of Brussels, where people write hundreds of messages on the ground to remember the victims of Tuesday's attack, Tuesday, March 22, 2016. Bombs exploded at the Brussels airport and one of the city's metro stations Tuesday, killing and wounding scores of people, as a European capital was again locked down amid heightened security threats. (AP Photo/Martin Meissner)

by: Associated Press

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People light candles at a memorial set up outside the stock exchange in Brussels on Tuesday, March 22, 2016. Explosions, at least one likely caused by a suicide bomber, rocked the Brussels airport and subway system Tuesday, prompting a lockdown of the Belgian capital and heightened security across Europe. (AP Photo/Geert Vanden Wijngaert)

by: Associated Press

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People bring flowers and candles to mourn at the Place de la Bourse in the center of Brussels, Tuesday, March 22, 2016. Bombs exploded at the Brussels airport and one of the city's metro stations Tuesday, killing and wounding scores of people, as a European capital was again locked down amid heightened security threats. (AP Photo/Martin Meissner)

by: Associated Press

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President Barack Obama, first lady Michelle, daughters Sasha, second from left, and Malia, far left, stand with Cuba's President Raul Castro, right, during a moment of silence for the victims of attacks in Brussels, Belgium, before the start of an exhibition baseball game between the Tampa Bay Rays and the Cuban National team at Estadio Latinoamericano in Havana, Cuba, Tuesday, March 22, 2016. (Ismael Francisco/Cubadebate via AP)

by: Associated Press

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The blown out facade of the terminal is seen as an ambulance leaves Zaventem airport, one of the sites of two deadly attacks in Brussels, Belgium, Tuesday, March 22, 2016. Authorities in Europe have tightened security at airports, on subways, at the borders and on city streets after the attacks Tuesday on the Brussels airport and its subway system. (AP Photo/Peter Dejong)

by: Associated Press

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The Belgian flag is projected on Rome's historical Trevi Fountain to honor the victims of the deadly attacks at Brussels airport and subway, Tuesday, March 22, 2016. Explosions, at least one likely caused by a suicide bomber, rocked the Brussels airport and its subway system prompting a lockdown of the Belgian capital and heightened security across Europe. (AP Photo/Andrew Medichini)

by: Associated Press

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Members of the New York National Guard patrol Penn Station, Tuesday, March 22, 2016, in New York. Authorities are increasing security throughout New York City following explosions at the airport and subway system in Brussels. (AP Photo/Mark Lennihan)

by: Associated Press

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People put candles on painted hearts with the Belgian colors to mourn for the victims at the place de la Bourse in the center of Brussels, Tuesday, March 22, 2016. Bombs exploded at the Brussels airport and one of the city's metro stations Tuesday, killing and wounding scores of people, as a European capital was again locked down amid heightened security threats. (AP Photo/Martin Meissner)

by: Associated Press

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A man lights a candle at a memorial outside the stock exchange in Brussels on Tuesday, March 22, 2016. Explosions, at least one likely caused by a suicide bomber, rocked the Brussels airport and subway system Tuesday, prompting a lockdown of the Belgian capital and heightened security across Europe. (AP Photo/Geert Vanden Wijngaert)

by: Associated Press

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A young girl looks out of the window of a bus after being evacuated from Brussels airport, after explosions rocked the facility in Brussels, Belgium, Tuesday March 22, 2016. Authorities locked down the Belgian capital on Tuesday after explosions rocked the Brussels airport and subway system, killing at least 13 people and injuring many more. Belgium raised its terror alert to its highest level, diverting arriving planes and trains and ordering people to stay where they were. Airports across Europe tightened security. (AP Photo/Geert Vanden Wijngaert)

by: Associated Press

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A woman is evacuated in an ambulance by emergency services after a explosion in a main metro station in Brussels on Tuesday, March 22, 2016. Explosions rocked the Brussels airport and the subway system Tuesday, killing at least 13 people and injuring many others just days after the main suspect in the November Paris attacks was arrested in the city, police said. (AP Photo/Virginia Mayo)

by: Associated Press

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The Palace of Culture, right, the tallest building in the Polish capital, is lit in the colors of the Belgian flag in solidarity with the victims of the attacks in Brussels, in Warsaw, Poland, on Tuesday March 22, 2016.(AP Photo/Czarek Sokolowski)

by: Associated Press

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Passengers check into their flights near a security checkpoint sign at O'Hare International Airport on Tuesday, March 22, 2016 in Chicago. The airport attack in Brussels highlights one of the most vulnerable stages of aviation security: the time travelers spend between the curb and the checkpoint. (AP Photo/Teresa Crawford)

by: Associated Press

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People mourn for the victims at Place de la Bourse in the center of Brussels, Tuesday, March 22, 2016. Bombs exploded at the Brussels airport and one of the city's metro stations Tuesday, killing and wounding scores of people, as a European capital was again locked down amid heightened security threats. (AP Photo/Martin Meissner)

by: Associated Press

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People walk away from Brussels airport after explosions rocked the facility in Brussels, Belgium Tuesday March 22, 2016. Explosions rocked the Brussels airport and the subway system Tuesday, just days after the main suspect in the November Paris attacks was arrested in the city, police said. (AP Photo/Geert Vanden Wijngaert)

by: Associated Press

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Metro-North Railroad police officers patrol Grand Central Terminal, in New York, Tuesday, March 22, 2016. Authorities are increasing security throughout New York City following explosions at the airport and subway system in the Belgian capital of Brussels. (AP Photo/Richard Drew)

by: Associated Press

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Nagyardei Stadium is illuminated with the Belgian national colours in Debrecen, 226 kms east of Budapest, Hungary, Tuesday, March 22, 2016 to pay tribute to victims of the terrorist attacks committed earlier Tuesday in Brussels, the capital of Belgium. Dozens of people were killed and more than 200 injured when bombs were detonated at Brussel's Zaventem international airport and at a metro station of the city. (Balazs Mohai/MTI via AP)

by: Associated Press

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The blown out facade of the terminal is seen as a fire truck drives down the ramp at Zaventem airport, one of the sites of two deadly attacks in Brussels, Belgium, Tuesday, March 22, 2016. Authorities in Europe have tightened security at airports, on subways, at the borders and on city streets after the attacks Tuesday on the Brussels airport and its subway system. (AP Photo/Peter Dejong)

by: Associated Press

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A memorial to attack victims with a Belgian flag and flowers is set up outside the stock exchange in Brussels on Tuesday, March 22, 2016. Explosions, at least one likely caused by a suicide bomber, rocked the Brussels airport and subway system Tuesday, prompting a lockdown of the Belgian capital and heightened security across Europe. (AP Photo/Geert Vanden Wijngaert)

by: Associated Press

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The Eiffel Tower is illuminated with the Belgium national colors black, yellow and red in honor of the victims of the today's attacks at the airport and the metro station in Brussels, in Paris, Tuesday, March 22, 2016. Explosions, at least one likely caused by a suicide bomber, rocked the Brussels airport and its subway system Tuesday, prompting a lockdown of the Belgian capital and heightened security across Europe. (AP Photo/Thibault Camus)

by: Associated Press

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People holding a banner reading "I am Brussels" behind flowers and candles to mourn for the victims at Place de la Bourse in the center of Brussels, Tuesday, March 22, 2016. Bombs exploded at the Brussels airport and one of the city's metro stations Tuesday, killing and wounding scores of people, as a European capital was again locked down amid heightened security threats. (AP Photo/Martin Meissner)

by: Associated Press

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People react outside Brussels airport after explosions rocked the facility in Brussels, Belgium Tuesday March 22, 2016. Explosions rocked the Brussels airport and the subway system Tuesday, just days after the main suspect in the November Paris attacks was arrested in the city, police said. (AP Photo/Geert Vanden Wijngaert)

by: Associated Press

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A man walks by solidarity messages written in chalk outside the stock exchange in Brussels on Tuesday, March 22, 2016. Explosions, at least one likely caused by a suicide bomber, rocked the Brussels airport and subway system Tuesday, prompting a lockdown of the Belgian capital and heightened security across Europe. At least 26 people were reported dead. (AP Photo/Geert Vanden Wijngaert)

by: Associated Press

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A pair of Metro-North Railroad Police officers patrol in New York's Grand Central Terminal, Tuesday, March 22, 2016. Authorities are increasing security throughout New York City following explosions at the airport and subway system in the Belgian capital of Brussels. (AP Photo/Richard Drew)

by: Associated Press

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People holding a banner reading "I am Brussels" behind flowers and candles to mourn for the victims at Place de la Bourse in the center of Brussels, Tuesday, March 22, 2016. Bombs exploded at the Brussels airport and one of the city's metro stations Tuesday, killing and wounding scores of people, as a European capital was again locked down amid heightened security threats. (AP Photo/Martin Meissner)

by: Associated Press

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A man lights a candle next to the iconic statue of Manneken Pis outside the stock exchange in Brussels on Tuesday, March 22, 2016. Explosions, at least one likely caused by a suicide bomber, rocked the Brussels airport and subway system Tuesday, prompting a lockdown of the Belgian capital and heightened security across Europe. (AP Photo/Geert Vanden Wijngaert)

by: Associated Press

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A woman is evacuated in an ambulance by emergency services after a explosion in a main metro station in Brussels on Tuesday, March 22, 2016. Explosions rocked the Brussels airport and the subway system Tuesday, killing at least 13 people and injuring many others just days after the main suspect in the November Paris attacks was arrested in the city, police said. (AP Photo/Virginia Mayo)

by: Associated Press

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A woman places candles in the shape of a heart outside the stock exchange in Brussels on Tuesday, March 22, 2016. Explosions, at least one likely caused by a suicide bomber, rocked the Brussels airport and subway system Tuesday, prompting a lockdown of the Belgian capital and heightened security across Europe. At least 26 people were reported dead. (AP Photo/Geert Vanden Wijngaert)

by: Associated Press

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People holding a banner reading "I am Brussels" behind flowers and candles to mourn for the victims at Place de la Bourse in the center of Brussels, Tuesday, March 22, 2016. Bombs exploded at the Brussels airport and one of the city's metro stations Tuesday, killing and wounding scores of people, as a European capital was again locked down amid heightened security threats. (AP Photo/Martin Meissner)

by: Associated Press

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House Speaker Paul Ryan of Wis., far left, is surrounded by his security detail as he arrives on Capitol Hill in Washington, Tuesday, March 22, 2016. Deadly explosions ripped through the Brussels airport and a subway station Tuesday during the morning rush hour, only days after the prime suspect in the Paris terror attacks Salah Abdeslam was arrested in Brussels. (AP Photo/J. Scott Applewhite)

by: Associated Press

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Police and rescue teams are pictured outside the metro station Maelbeek in Brussels, Tuesday, March 22, 2016. Explosions, at least one likely caused by a suicide bomber, rocked the Brussels airport and its subway system Tuesday, prompting a lockdown of the Belgian capital and heightened security across Europe. (AP Photo/Martin Meissner)

by: Associated Press

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People take selfies in front of the Brandenburg Gate, illuminated with the Belgian national flag in reaction to the Brussels attacks, in Berlin, Germany, Tuesday, March 22, 2016. (AP Photo/Markus Schreiber)

by: Associated Press

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A man looks at flowers and messages outside the stock exchange in Brussels on Tuesday, March 22, 2016. Explosions, at least one likely caused by a suicide bomber, rocked the Brussels airport and subway system Tuesday, prompting a lockdown of the Belgian capital and heightened security across Europe. At least 26 people were reported dead. (AP Photo/Geert Vanden Wijngaert)

by: Associated Press

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People light candles in the shape of a heart outside the stock exchange in Brussels on Tuesday, March 22, 2016. Explosions, at least one likely caused by a suicide bomber, rocked the Brussels airport and subway system Tuesday, prompting a lockdown of the Belgian capital and heightened security across Europe. (AP Photo/Geert Vanden Wijngaert)

by: Associated Press

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A man walks by solidarity messages written in chalk outside the stock exchange in Brussels on Tuesday, March 22, 2016. Explosions, at least one likely caused by a suicide bomber, rocked the Brussels airport and subway system Tuesday, prompting a lockdown of the Belgian capital and heightened security across Europe. At least 26 people were reported dead. (AP Photo/Geert Vanden Wijngaert)

by: Associated Press

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Nagyardei Stadium is illuminated with the Belgian national colours in Debrecen, 226 kms east of Budapest, Hungary, Tuesday, March 22, 2016 to pay tribute to victims of the terrorist attacks committed earlier Tuesday in Brussels, the capital of Belgium. Dozens of people were killed and more than 200 injured when bombs were detonated at Brussel's Zaventem international airport and at a metro station of the city. (Balazs Mohai/MTI via AP)

by: Associated Press

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Smoke billows from the Zaventem Airport after a controlled explosion in Brussels, Tuesday, March 22, 2016. Bombs struck the Brussels airport and one of the city's metro stations Tuesday, killing and wounding dozens of people, as a European capital was again locked down amid heightened security threats. (AP Photo/Michel Spingler)

by: Associated Press

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After attacks in Brussels, a candle wrapped in a ribbon in the colors of the Belgium national flag and flowers are placed on a table inside the Belgium Embassy in Berlin, Germany, Tuesday, March 22, 2016. (AP Photo/Markus Schreiber)

by: Associated Press

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Forensic staff leave the metro station Maelbeek in Brussels, Tuesday, March 22, 2016. Explosions, at least one likely caused by a suicide bomber, rocked the Brussels airport and its subway system Tuesday, prompting a lockdown of the Belgian capital and heightened security across Europe. (AP Photo/Martin Meissner)

by: Associated Press

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A German police officer guards a terminal of the airport in Frankfurt, Germany, Tuesday, March 22, 2016, when various explosions hit the Belgian capital Brussels killing several people. (AP Photo/Michael Probst)

by: Associated Press

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Passengers leave a gym where they took shelter after the explosions, near the Zaventem Airport in Brussels, Tuesday, March 22, 2016. Bombs struck the Brussels airport and one of the city's metro stations Tuesday, killing and wounding dozens of people, as a European capital was again locked down amid heightened security threats. (AP Photo/Michel Spingler)

by: Associated Press

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The Brandenburg Gate is illuminated with the Belgium national flag in reaction to the Brussels attacks, in Berlin, Germany, Tuesday, March 22, 2016. (AP Photo/Markus Schreiber)

by: Associated Press

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People bring flowers and candles to mourn at the Place de la Bourse in the center of Brussels, Tuesday, March 22, 2016. Bombs exploded at the Brussels airport and one of the city's metro stations Tuesday, killing and wounding scores of people, as a European capital was again locked down amid heightened security threats. (AP Photo/Martin Meissner)

by: Associated Press

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Chairman of the Danish Parliament, Pia Kjaersgaard, with flowers for the victims of the Brussels attacks, at the Belgium Embassy in Copenhagen Tuesday, March 22, 2016. Bombs exploded at the Brussels airport and one of the city's metro stations Tuesday, killing and wounding dozens of people, as a European capital was again locked down amid heightened security threats. The Islamic State group claimed responsibility for the attacks. (Philip Davali/POLFOTO via AP) DENMARK OUT

by: Associated Press

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A woman is evacuated in an ambulance by emergency services after a explosion in a main metro station in Brussels on Tuesday, March 22, 2016. Explosions rocked the Brussels airport and the subway system Tuesday, killing at least 13 people and injuring many others just days after the main suspect in the November Paris attacks was arrested in the city, police said. (AP Photo/Virginia Mayo)

by: Associated Press

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The Belgium and British flag fly at half staff above Downing Street in London, following the attacks in Brussels, Tuesday, March, 22, 2016. Authorities in Europe and beyond have tightened security at airports, on subways, at the borders and on city streets after deadly attacks Tuesday on the Brussels airport and its subway system. (AP Photo/Kirsty Wigglesworth)

by: Associated Press

88 of 92

The blown out facade of the terminal is seen as an ambulance leaves Zaventem airport, one of the sites of two deadly attacks in Brussels, Belgium, Tuesday, March 22, 2016. Authorities in Europe have tightened security at airports, on subways, at the borders and on city streets after the attacks Tuesday on the Brussels airport and its subway system. (AP Photo/Peter Dejong)

by: Associated Press

89 of 92

Two soldiers from the Belgian Army patrol outside EU headquarters as EU flags fly at half mast after an explosion in Brussels on Tuesday, March 22, 2016. Explosions, at least one likely caused by a suicide bomber, rocked the Brussels airport and subway system Tuesday, prompting a lockdown of the Belgian capital and heightened security across Europe. At least 26 people were reported dead. (AP Photo/Virginia Mayo)

by: Associated Press

90 of 92

In this image provided by the Belgian Federal Police in Brussels on Tuesday, March 22, 2016 of three men who are suspected of taking part in the attacks at Belgium's Zaventem Airport. The man at right is still being sought by the police and two others in the photo that the police issued were according to a the Belgian Prosecutors 'probably' suicide bombers. Bombs exploded at the Brussels airport and one of the city's metro stations Tuesday, killing and wounding scores of people, as a European capital was again locked down amid heightened security threats. (Belgian Federal Police via AP)

by: Associated Press

91 of 92

A writing on the asphalt reads "Brussels forever" at the place de la Bourse in the center of Brussels, where people write hundreds of messages on the ground to remember the victims of todays attack, Tuesday, March 22, 2016. Bombs exploded at the Brussels airport and one of the city's metro stations Tuesday, killing and wounding scores of people, as a European capital was again locked down amid heightened security threats. (AP Photo/Martin Meissner)

by: Associated Press

92 of 92

A pair of Metro-North Railroad Police officers patrol in New York's Grand Central Terminal, Tuesday, March 22, 2016. Authorities are increasing security throughout New York City following explosions at the airport and subway system in the Belgian capital of Brussels. (AP Photo/Richard Drew)

by: Associated Press

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