Obama refused to concede that his opposition to the increase in U.S. troop strength was wrong. He said President George W. Bush did not put any pressure on the Iraqi government to achieve political reconciliation.

"We have gone through five years of mismanagement of this war that I thought was disastrous, and the president wanted to double down and continue an open-ended policy," he said.

The interview was Obama's first with Fox's Bill O'Reilly.

Obama said he considers Iran a "major threat" and said if Tehran acquires nuclear weapons it would be a "game changer." He said the use of military force there is not "off the table" as far as he is concerned.

The first part of the interview aired Thursday. Three more segments are to be broadcast next week, Fox said.

The interview took place in York, Pa., after Obama held a meeting with voters. Obama attended a fundraiser Thursday morning in Pittsburgh at which Franco Harris, a former running back with the Steelers and a delegate to the Democratic Convention, played host.