BAGHDAD (AP) — Defense Secretary Robert Gates said today that although no additional U.S. combat brigades are to withdraw from Iraq this year, he expects the U.S. combat role to keep shrinking.

“We are clearly in a mission transition,” he told reporters on an overnight flight here from Washington.

U.S. troops will increasingly play a backup role, Gates said, as Iraqi security forces take on more of the responsibility for fighting an insurgency that has lost much of its power and influence over the past year.

“The areas in which we are seriously engaged (in fighting) will, I think, continue to narrow,” Gates said.

Iraq currently has primary responsibility for security in 11 of its 18 provinces. It regained responsibility for Anbar province, at one time the stronghold of the Sunni insurgency, a few weeks ago.