(CNN) -- A German citizen of Afghan descent was the source of much of the information on a potential "Mumbai-style" terror plot in Europe, a German counterterrorism official said Wednesday. The man, Ahmed Sidiqi, was detained in Kabul in July and transferred to U.S. custody where he has "revealed details about the terror plot," said the official, who did not want to be named because he is not authorized to talk to the media. The man and several other Germans traveled from Hamburg to the Afghan-Pakistan border area in 2009, where he joined the Islamic Movement of Uzbekistan, an extremist group allied with al Qaeda, German intelligence officials said.
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NEW: Clapper: We're not going to comment on specific intelligence
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Man talks about a "Mumbai-style" attack in Europe, official says
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He attended the same mosque in Hamburg as 9/11 hijacker Atta
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Europe plot is one factor in the increase in drone attacks in Pakistan
"As we have repeatedly said, we know al Qaeda wants to attack @placeholder and the United States."