German authorities, acting on tips from the FBI, also said that they had detained at least one man in connection with Tuesday's attacks and were searching for another.

In France, special anti-terrorism prosecutors tried to find links with militant Islamic networks in their country, while police in Rome re-opened the case of a theft of uniforms and badges belonging to two American Airlines pilots in April.

Two of the men identified by Hamburg police as having perished in the attacks were Mohamed Atta and Marwan Alshehhi, both from the United Arab Emirates. Both had earlier been named as former students of a Florida flight school and are suspected of having flown two of the hijacked jets.

The German authorities indicated that they'd made no immediate links to Osama bin Laden, the Saudi millionaire who was identified Thursday by U.S. Secretary of State Colin Powell as a prime suspect in the attacks. However, chief federal prosecutor Kay Nehm said that they did have links to other terror cells abroad.

Meanwhile, Attorney General John Ashcroft said the FBI has determined that a total of 18 hijackers were on the four hijacked planes. There were five on each of two planes and four each on the other two. U.S. officials said all have been identified the hijackers but they have not released any identities.

The president of Hamburg Technical University, where the two men studied until last year, said he had been informed that Atta was aboard the plane that crashed into World Trade Center Tower One, and that Alshehhi was the jet that struck the other tower 20 minutes later.

German investigators believe the two men, and a third suspect who also died, belonged to a terror group formed ''with the aim of carrying out serious crimes together with other Islamic fundamentalist groups abroad, to attack the United States in a spectacular way through the destruction of symbolic buildings,'' Nehm told reporters in Karlsruhe.

In the United Arab Emirates authorities called in people familiar with a Emirates man named Marwan Alshehhi for questioning, officials said Thursday.

Quoting an unidentified official source, the state-run Emirates News Agency said security authorities had yet to confirm that the Emirates national identified as Marwan Alshehhi was the person with the same name suspected by German police.

Another Emirates official, speaking to The Associated Press on condition of anonymity, said all those called in, including relatives and friends of Alshehhi, were released following questioning. The official would provide no further details.

Nehm said the man being sought had an Arab background and was suspected of murder and air piracy as well as membership in a terrorist organization. Nehm gave no further details.

A spokeswoman from his office later said a man had been taken into custody early Thursday during a search. Also, local police announced the arrest of a Hamburg airport employee. Nehm's office refused to clarify whether this was the same man.

Details surrounding the two named suspects, Atta and Alshehhi, remained sketchy.

The two men had been registered for several years as residents of Hamburg, a port city of 1.7 million people, including 80,000 Muslims. Police searched an apartment where the two formerly resided, but said it had not been inhabited since February, and had been renovated, making the search for evidence difficult.

A neighbor said he had occasionally met the men in the stairway.

''They seemed like normal people. There were maybe three to five people there,'' said the man, who refused to give his name.

Alshehhi, 23, studied one year at the Technical University and Atta, 33, studied eight years, completing one degree and starting a second, university president Christian Nedess said.

He declined to say what the men had studied, but said it wouldn't have given them technical knowledge that would have aided in the terror attack.

Authorities informed Nedess that other students also were being investigated.

According to Hamburg authorities, Alshehhi left Germany for the United States on May 2; it was unclear when Atta left. It wasn't their first trip.

The two men stayed briefly with a former employee of Huffman Aviation, the Venice, Fla., flight school where they studied beginning in July 2000.