A mosque which used to be a meeting place for the September 11 attackers has been closed, German authorities said.
Officials said that the Taiba mosque in Hamburg and a cultural association connected with it have been banned.
The prayer house, formerly known as al-Quds mosque, used to be a meeting and recruiting point for some of the September 11 attackers before they moved to the US.
Weekly news magazine Focus reported that the mosque had again become the city's "main centre of attraction for the jihad scene".
According to the report, some members who belonged to the Taiba group and prayed at the mosque have moved on to a radical training camp in Uzbekistan.
"We have closed the mosque because it was a recruiting and meeting point for Islamic radicals who wanted to participate in so-called jihad or holy war," said Frank Reschreiter, a spokesman for Hamburg's state interior ministry.
He added that 20 police officers were searching the building and had confiscated material, including several computers. He was not aware of any arrests.
Mr Reschreiter said it was the first time the mosque had been closed, but it had been under observation by local intelligence officers for "quite a long time".