Hamburg's top security official called Wednesday for an inquiry into media claims that the US Central Intelligence Agency (CIA) deployed assassins in the city in 2004, DPA reported.
US magazine Vanity Fair said this week it would be publishing a story that the CIA sent a team from the private security firm Blackwater, now Xe, to Hamburg to "find, fix and finish" an alleged al-Qaeda fund-raiser, Mamoun Darkazanli, 51.
Christoph Ahlhaus, interior minister of Hamburg state, said he wanted the German government to check the claims out. Earlier, a Berlin spokesman said the government had it had no knowledge of such an operation.
On Monday, Hamburg prosecutors said they would study the claims.
Syrian-born Darkazanli, who has a German passport, was an associate of several of the Hamburg suicide attackers who used hijacked jets to kill almost 3,000 people on September 11, 2001 in New York, Washington and Pennsylvania. Germany investigated him but did not try him.
The Blackwater team allegedly kept Darkazanli under surveillance for weeks but withdrew when there was no order to assassinate him.
"I expect the federal government to contact the United States government and ask for a complete inquiry into the facts," said Ahlhaus in remarks to the German Press Agency dpa.
"If there is evidence that US organizations were operationally active in Germany in this way without the knowledge of their German counterparts, we can't just act as if nothing happened."
Ahlhaus, who supervises the state police and anti-subversion agency, said they knew nothing of such a mission.
Darkazanli continued to live openly in Hamburg after the September 11 attacks but his current whereabouts are unknown. Spain twice sought his extradition, but Germany refused. Allegedly he was European liaison and fund-raiser for al-Qaeda from 1993 to 1998.
Germany was earlier upset by the treatment of Khaled el-Masri, a German of Lebanese descent who says he was arrested in Macedonia in 2003 and flown by the CIA to Afghanistan, then freed in May 2004 without charge.