In his weekly radio address, Bush said "serious and complex challenges remain in Iraq," but he said "a major strategic shift has occurred" since the surge.

"While there's more to be done, sectarian violence, civilian deaths, and military deaths are down," said Bush. "Improvements in security have helped clear the way for political and economic progress."

Bush said U.S. and Iraqi forces have put al-Qaida in Iraq "on the defensive" and said "now we are working to deliver a decisive blow."

The president said the United States will continue to support Iraqi security forces and "transfer security responsibilities to them, and move over time into an overwatch role."

"The turnaround that our men and women in uniform have made possible in Iraq is a brilliant achievement," said Bush.