The last brigade of American combat troops left Iraq on Thursday, ending U.S. combat operations there and signalling a new chapter in the country's future.

The final convoy of troops, 360 members of the 4th Stryker Brigade, 2nd Infantry Division, crossed the southern border into Kuwait before dawn. They rode in a long line of heavily armoured military vehicles down the middle of Iraq's main north-south highway.

Their departure comes nearly two weeks before the official end of combat missions on Aug. 31.

U.S. Army soldiers from 2nd Battalion, 23rd Infantry Regiment, 4th Brigade, 2nd Infantry Division race toward the border from Iraq into Kuwait. The soldiers are part of the last combat brigade to leave Iraq as part of the drawdown of U.S. forces. (Maya Alleruzzo/Associated Press)

"When they told us they were going to do this, you didn't really grasp how important it was," said Lt. Steve DeWitt, who rode in the convoy.

"You know, how big of a deal this actually was, driving out of here … as the last combat battalion out of Iraq. It feels pretty good to be a part of it right now."

The brigade's departure marks the end of Operation Iraqi Freedom, the U.S. military campaign that began on March 20, 2003, and in which at least 4,415 American soldiers have been killed and nearly 32,000 injured.

Fewer than 6,000 combat troops are expected to complete the withdrawal next week.

Another 50,000 non-combat troops remain in Iraq for what the U.S. Department of Defence is calling Operation New Dawn. Their purpose is to help "move toward stability operations, advising, training and assisting the [Iraqi Special Forces] in building civil capacity in Iraq," the Defence Department said on its website.

They will carry weapons to defend themselves and accompany Iraqi troops on missions if asked. Special forces will continue to help Iraqis hunt for terrorists.

Freelance reporter Prashant Rao said many Iraqis are worried about what will happen after the U.S. combat mission ends.

"Security here still remains precarious," Rao said from Baghdad.

"Iraqis on the streets of several cities have told me and my colleagues today that they are concerned about their own security forces — that they are not ready or able to do the job."

On Tuesday, a suicide bomber blew himself up in a crowd of people waiting outside a military recruitment office in Baghdad, killing dozens of people.

Maj.-Gen. Stephen Lanza, the spokesman for U.S. forces in Iraq, said Thursday morning that Iraqi police and military are up to the task of keeping the country secure after the withdrawal is complete, but added the sooner the government is seated the calmer the country will be.

With files from The Associated Press