U.S. and Kurdish forces moved to take control of two key northern cities in Iraq on Friday as troops in the capital grappled with continued looting and civil disorder and girded for more possible suicide bomb attacks.

U.S. troops entered the key oil center of Kirkuk on Thursday and were moving in reinforcements to take control of the city, helping calm fears in Turkey after Kurdish fighters took the city in a bloodless rout of Iraqi forces.

Defense Secretary Donald Rumsfeld said late on Thursday some American troops were also moving into Iraq's third city of Mosul after signs of Iraqis surrendering in the area.

"Within recent hours I'm told that in Mosul there appears to be an opportunity for the regular Iraqi forces to turn in their weapons and no longer pose a threat, in which case Kurdish forces and U.S. forces in small numbers are in the process of moving into Mosul," he said.