US Defence Secretary Robert Gates told US soldiers yesterday that, with the end of combat missions declared, they were in the final phase of America's engagement in Iraq and history would judge if the invasion had been worthwhile.

On a visit to troops in Ramadi, scene of some of the fiercest fighting of the 7½-year war, Gates said he believed the soldiers should continue to get combat pay though their mission had changed to assisting Iraqi forces.

"Combat operations have ceased," he said. "We're still going to work with the Iraqis on counter-terrorism. We're still doing training, and advising and assisting. So I would say we have moved into the final phase of our engagement in Iraq."

Gates and Vice-President Joe Biden were in Iraq yesterday for a ceremony at which a new commander of US forces in Iraq began his tour of duty.

The change of command was a day after the formal end of the US combat mission launched by President Barack Obama's predecessor in the White House, George W Bush, in 2003.

Obama told Americans in a speech televised from the Oval Office that it was "time to turn the page" on Iraq.

About 50000 US soldiers will remain in Iraq until the end of next year in terms of an agreement between the US and Iraq.

The US forces will advise and assist Iraqi forces instead of leading the fight against a Sunni Islamist insurgency and the Shia militia.

Security remains a big worry in Iraq. Attacks against Iraqi security forces have been increasing, and there are concerns the end of US combat operations will leave a big gap for insurgents to exploit.