Hundreds have been killed in the fighting, and attempts at a ceasefire have so far failed to halt the bloodshed.

There were too many dead and wounded for hospital workers in the besieged town to deal with. Outside a hastily erected field hospital, Reuters television footage shows corpses lying in the street, wrapped in bloodstained white sheets.

The dead include small children, women and old men, a new born baby. Beside the corpses, there is a pile of body parts which no one has had time to deal with.

The U.S. military says its operations are precise and it does not target civilians or women and children.

"We are here in a small hospital and cannot cope with all the casualties," one doctor said. "The important thing now is to try and get the wounded out."

The U.S. military announced a unilateral ceasefire in Falluja on Friday to allow humanitarian access to the town west of Baghdad and facilitate peace talks. Fighting did not stop.

On Saturday, the U.S. offered a bilateral ceasefire, but again the fighting continued. Marines say they are only firing back when under attack and do not target women and children, but wounded civilians still fill the limited hospital beds.

It is difficult for journalists to access Falluja, surrounded by U.S. troops who launched a crackdown on insurgents in the town early this week. There are few independent assessments of damage.

An assessment by five international non-governmental organisations on Friday said 470 people had been killed in Falluja. Of 1,200 injured, it said 243 were women and 200 children. The groups said their estimate may be conservative.

"Dead bodies are lying in the streets. Ambulances are being shot at by snipers. Medical aid and supplies have been stopped by U.S. occupation forces," a statement from the NGOs said.

"The thousands of families who remain trapped in Falluja are running out of basic necessities like food and potable water. Hospitals and medical staff are overwhelmed, and are asking desperately for blood, oxygen and antiseptics."

In lulls between fighting, children play in Falluja's near-empty streets, jumping over puddles and rubbish.

"We were driving in the car and we got wounded, me in the shoulder, her in the head, her in the hand," said one small girl, pointing to other wounded children sitting around her in the clinic.

"Why are they doing this to us? We are a family, they shouldn't treat us like this."

Residents say the Marines shoot without concern for their targets. One doctor pointed to an ambulance outside the clinic whose windscreen and side was riddled with bullet holes.

"We went close to Abdulaziz mosque and evacuated some wounded, when a sniper fired at us," he said. "Our driver was killed and some of the wounded died."