The last U.S. combat brigade in Iraq has crossed into Kuwait, leaving Iraq ahead of the August 31 deadline, NBC news reported on Wednesday night.

U.S soldiers take up position during a patrol in Kerbala, 80 km south of Baghdad July 17, 2010. [Xinhua]

TV footage showed a convoy from the 4th Stryker Brigade of the 2nd Infantry Division crossing the Iraq-Kuwait border. The last vehicle traversed the border at about 3:53 a.m. Thursday local time and the border gate closed behind it.

The 4th Stryker Brigade reportedly has about 4,000 troops. CNN said after it leaves Iraq, there would be two other combat brigade inside Iraq, but they are in a transition process to become non-combat units, and would take on responsibilities of training Iraqi troops.

However, U.S. media quoted unnamed administration officials as saying the completion of withdrawal doesn't mean the end of combat mission. U.S. combat mission will end in Iraq on August 31 as scheduled.

U.S. President Barack Obama has set the end of August as the deadline to end combat operations in Iraq. Washington said that about 50,000 U.S. troops will remain in Iraq to conduct support and training missions.

In a letter posted Wednesday on the White House website, Obama hailed the end of combat operations, but didn't mention the last combat troops out of Iraq on the same day.

"I'm pleased to report that... our combat mission will end this month, and we will complete a substantial drawdown of our troops," Obama said.

State Department spokesman Philip Crowley told MSNBC the end of combat operations is a "historic moment." The U.S. mission in Iraq will be transformed into a mainly diplomatic one as combat troops leaves.

"We're not ending our involvement in Iraq. We will have important work to do. This is a transition. This is not the end of something. It's a transition to something different. We have a long-term commitment to Iraq," said Crowley.

When Obama took office last year, there were about 144,000 U.S. troops inside Iraq. After he decided to pull troops out of that country and send more soldiers to Afghanistan, about 90,000 troops have been withdrawn from Iraq.