"We have 13 killed and 13 wounded," said doctor Bilal Jassem at Fallujah's main hospital without indicating if the casualties were civilians or fighters.

The same toll was given by Lieutenant Walid Mohammed of the Iraqi police.

The US military said earlier that it targeted insurgents in Fallujah on Thursday night with artillery and air fire after they attacked a marine position in the city with mortars, rocket-propelled grenades and small arms.

Marines first responded to the attack on their position with tanks and artillery fire, it said, adding that there were no marine casualties and "no information about any insurgent losses."

Residents said they heard loud explosions that appeared to come from the Shuhada neighbourhood in the south of the city, the target of previous US air strikes.

"I heard a very powerful explosion around 10:30 pm (1830 GMT) coming from the Shuhada neighbourhood," said a resident on condition of anonymity.

The US military has conducted at least seven air strikes over the past month on suspected hideouts of loyalists of alleged al-Qaeda operative Abu Mussab al-Zarqawi, most of them in southern Fallujah.

Two raids in early July killed 23 people.

Zarqawi, who is blamed for some of the bloodiest car bombs and attacks in Iraq, has a 25-million-dollar US bounty on his head.