Deutsche Welle reported German authorities had received information that Islamic terrorists were planning suicide car bomb attacks in early 2004 in Hamburg and Frankfurt.
Hamburg state Interior Minister Dirk Nockemann said their targets included the military hospital in Frankfurt and a U.S. military airport in Frankfurt.
German Interior Minister Otto Schily on Wednesday confirmed that the tip-off had come from the U.S. Central Intelligence Agency.
A month ago, police arrested a suspected Algerian militant in Hamburg as part of a Europe-wide probe into a network believed to be recruiting Islamists for suicide attacks in Iraq.
A spokesman at the Hamburg military hospital said no U.S. soldiers were currently being treated there, but said American soldiers injured in Iraq had undergone treatment at the hospital in the past.