"Fierce clashes erupted in the afternoon between Iraqi military forces and insurgents in the Nazzal neighborhood in southern Fallujah and in the center area of the city, killing two soldiers and wounding three others," local witnesses told Xinhua by telephone.

In Ramadi, some 110 km west of Baghdad, insurgents clashed with U.S. troops in the center of the city for several hours in the morning, local resident said.

However, it was not clear whether there were any casualties on both sides as the U.S. troops blocked all the entrances of the city, they said.

Iraq's western Anbar province, where Ramadi and Fallujah locate, has long been restive as insurgents frequently attack the U.S. and Iraqi security forces.