There is evidence that there is a network and it [Hamburg] is a centre of the network

German official

The connections were identified after investigators pieced together information from apartment searches, intercepted phone calls and suspect bank accounts.

The federal prosecutors who are heading the German side of the investigations had previously said there was no link between the Hamburg group and Bin Laden who is accused by the United States and its allies of masterminding the 11 September attacks.

Three of the 19 suspected hijackers on board the planes which plunged into New York, Washington and Pennsylvania, had been living in Hamburg before the attacks.

Recruitment network

Mohammed Atta, Marwan al-Shehhi and Ziad Jarrah were enrolled at technical university in the city.

Mohammed Atta - a suspected hijacker - studied in Hamburg

"All the clues point to Bin Laden's network and bear its signature," said government spokesman Uwe-Karsten Heye.

Sources close to the investigation say they do not believe that the attacks were planned there but that it was the heart of a recruitment network.

"We have a lot of links, we have a lot of clues. There is evidence that there is a network and it [Hamburg] is a centre of the network," an unnamed source said.

Intelligence services are also reported to have intercepted a telephone conversation between Bin Laden associates on the day of the attack which indicated 30 people may have been involved.

Contact man

Lists of suspect bank accounts appear to have identified a 55-year-old Indonesian man as Bin Laden's contact in the city.

The suspected hijackers were thought to be part of a German-based network

The list, obtained by Reuters news agency, includes 20 German addresses as well as many in the United States.

A federal warrant has been issued for two men - German-Moroccan Said Bahaji and Ramzi Binalshibh from Yemen.

They are thought to have formed a terrorist group with the three suspected hijackers and helped to plan the attacks.

As part of the investigations, authorities have frozen 214 bank accounts with a total value of 8m deutschemarks ($3.75m) belonging to people thought to be connected to the attackers.