Israeli police questioned Prime Minister Ehud Olmert about funds raised by an American supporter for municipal and party elections in 1999 and 2002, Olmert's office said in a statement.
It said Olmert, a Jerusalem ex-mayor who became premier in 2006, was cooperating with the probe. The statement did not say whether police suspect Olmert of using the fundraiser's money illicitly.
Asked whether Olmert denies wrongdoing in the case, as he has in three other graft investigations against him, a spokeswoman declined comment.