The final convoy of the Army's 4th Stryker Brigade Combat Team, based at Fort Lewis, Wash., crossed the border into Kuwait early Thursday (6:30 p.m. EDT Wednesday), NBC News reported.
"Operation Iraqi Freedom ends on your watch!" Col. John Norris -- head of the 4th Stryker Brigade, 2nd Infantry Division -- told his troops as they prepared to leave Iraq, The Washington Post reported.
The departure brings the curtain down on active combat operations that began in March 2003, when the United States and its allies invaded Iraq. More than 4,400 U.S. troops and an undetermined number of Iraqis -- variously estimated at anywhere from tens of thousands to hundreds of thousands -- have been killed in the war.
U.S. State Department spokesman P.J. Crowley told MSNBC the end of Operation Iraqi Freedom is a "historic moment" but not the end of the U.S. mission in Iraq.
"We have a long-term commitment to Iraq," Crowley said.
The United States will have six brigades in Iraq by the end of August, the Post said. They will mostly be conventional combat brigades charged with training Iraqi troops.
Under a status of forces agreement negotiated between the United States and Iraq during the administration of former President George W. Bush, all U.S. troops are to leave Iraq by Dec. 31, 2011.