BAGHDAD Cheered wildly by U.S. troops, President Barack Obama flew unannounced into Iraq today and promptly declared it is time for Iraqis to "take responsibility for their country" after America's commitment of six years and thousands of lives."

"You have given Iraq the opportunity to stand on its own as a democratic country," the president said as he made a brief inspection of a war he opposed as candidate and now vows to end as commander in chief. "That is an extraordinary achievement."

A total of 4,266 U.S. troops have lost their lives in Iraq since March 2003, and Obama said American forces had "performed brilliantly ... under enormous strain."

"It is time for us to transition to the Iraqis," he said as an estimated 600 troops cheered. "They need to take responsibility for their country."

Obama flew unannounced into Iraq and was shielded by heavy security from the moment he stepped off a gleaming white and blue Air Force One.

The plane touched down a few hours after a car bombing, in a Shiite neighborhood of the capital city.

Obama spoke favorably of political progress but also expressed concern that recent gains could deteriorate with the upcoming national elections.

"It's important for us to use all of our influence to encourage the parties to resolve these issues in ways that are equitable. I think that my presence here can help do that," he said.