German prosecutors say they have exposed an Islamic terrorist network in the country.
The head of the German federal prosecutors office, Mr Kay Nehm, said he had begun an investigation into "several" suspects accused of forming a terrorist network in Germany since January.
He said the inquiry was based in part on information provided by the US Federal Bureau of Investigations.
Earlier German police detained an airport worker in connection with an investigation into the terror attacks. Police declined to identify the man and did not say what his job had been.
"We have in the search for a suspect of Moroccan origin searched an apartment in Hamburg and provisionally detained one person, a man," head of the Hamburg state police Mr Gerhard Mueller said.
Mr Nehm said that the Arab men were believed to have formed a terrorist group with "fundamentalist Islamic beliefs" aimed at co-operating with foreign terrorist networks in "destroying symbolically important buildings in a spectacular fashion".
He said that two of the members were believed to have been aboard the first flight that crashed into the World Trade Center in New York while a third was on the hijacked plane that crashed soon after in Pennsylvania.
Mr Nehm said the Hamburg bureau of Germany's Federal Crime Office had learned that all three men had lived for a time in the city.
FBI information had led Hamburg police to conduct raids overnight in nine local apartments considered to have links to suspects in the assault on America.
Hamburg state Interior Minister Mr Olaf Scholz identified two of the primary suspects as Mr Mohamed Atta (33) who was registered on American Airlines flight 11, and Mr Marwan Al-Shehhi (23) who was on the passenger list of United Airlines flight 175.
Mr Scholz said the two men were enrolled at the Technical University Hamburg-Harburg to study ship construction and electronics. He said: "It is not clear if that is what they really studied".
AFP