'You've just killed a family because you didn't fire a warning shot soon enough'

As a blue Toyota van raced towards an intersection held by American troops, Captain Ronny Johnson grew increasingly concerned. He radioed to one of his forward platoons, giving the order: "Fire a warning shot." The vehicle kept coming, so, with increasing urgency, he told the platoon to shoot a machine-gun round into its radiator. "Stop [messing] around!" Capt Johnson yelled into the radio when he saw no action being taken. Then he shouted at the top of his voice "Stop him, Red 1, stop him!"

The hail of gunfire that followed resulted in the deaths of up to 10 Iraqi women and children, including five under the age of five.

Sharply conflicting accounts of the tragedy at a military checkpoint near Najaf on Monday evening were still circulating yesterday when American troops shot dead another civilian at a roadblock. He was unarmed.

American commanders admitted that their soldiers had killed seven women and children but their first reaction was to defend their troops, saying they opened fire after warning shots, including one into the vehicle's engine, were ignored. The men involved did "absolutely the right thing", said General Peter Pace, vice-chairman of the joint chiefs of staff. "Our soldiers on the ground have an absolute right to defend themselves."

But William Branigin, a journalist for The Washington Post who witnessed the incident, filed a graphic account of Capt Johnson's interchange with his platoon. The reporter said 10 people were killed, and that the first shots fired included 25mm high-explosive cannon shells from one or more Bradley fighting vehicles, which tore into the four-wheel-drive.

He claimed that Capt Johnson, a veteran of the 1991 Gulf War, after peering into his binoculars from the intersection where he was positioned, screamed at his platoon leader: "You just [expletive] killed a family because you didn't fire a warning shot soon enough!"

Afterwards, reported Mr Branigin, the soldiers gave the survivors 10 body bags to recover the remains and offered them money in compensation.

An army medic present told Mr Branigin: "It was the most horrible thing I've ever seen and I hope I never see it again."

US Central Command said Monday's killings and yesterday's shooting, which happened when a white pick-up truck failed to stop at a checkpoint 20 miles from Nasiriyah, were being investigated. But it was maintaining its unapologetic stance. "There will be occasions where civilians will be put in harm's way," said Brigadier General Vincent Brooks. Another spokesman blamed the Najaf deaths on Saddam Hussein.

"This is yet another incident in a trend of this regime using civilians, in this case innocent women and children, in order to cause harm to coalition forces," said Capt Frank Thorp. "The blood of this incident is on the hands of this regime."

To others, the deaths indicate how jittery and trigger-happy American troops have become since an Iraqi soldier blew himself up at a roadblock on Saturday, killing four Americans. "I thought it was a suicide bomb," said one of the soldiers who opened fire.

Capt Johnson was quoted by The Washington Post as saying that he thought the Toyota driver might have been a suicide bomber. "All the other vehicles stopped and turned around when they saw us," he said. "But this one kept on coming."

These are the first civilian deaths for which the Anglo-American forces have admitted responsibility, but "embedded" journalists have seen evidence of several more, usually when Iraqis have approached troop positions at night.

Predictions that the Iraqi population would welcome British and American troops have proved wide of the mark. A Pentagon spokesman's comment that "everyone is now seen as a combatant until proven otherwise" means gaining civilian support will be harder than ever. Asked if the checkpoint killings undermined attempts to win over locals, a British Army spokesman said: "It does indeed."

Commanders insist that the rules of engagement have not changed, but new procedures have been ordered in response to the suicide bombing. Drivers and passengers at checkpoints will be ordered out of vehicles with their hands raised, and will be searched. Cars and lorries will no longer be permitted to cross through American and British convoys; any vehicle blocking traffic will be pushed aside.

And if civilians approach troops with their hands in their pockets and fail to respond, first to a shouted command and then to a warning shot, they will be killed, US officials say.

American forces have traditionally taken a more aggressive, arms-length approach towards civilian populations than other Western armies. This conflicts with their desire to appear as "liberators" in Iraq. On peace-keeping duties in Kosovo, for example, US troops were ordered to wear full battle gear at all times, unlike every other national contingent.

James Dingley, a lecturer on terrorism at the University of Ulster, contrasted the US approach with that of the British, whose Northern Ireland experience means they are accustomed to closer contact with civilians. "Americans lived in their fortified villages and never mixed with anybody [in the Balkans]," he said. "They had virtually no comprehension of the locals ... and developing empathy with them."