A military investigation has reportedly concluded that US Marines embarked on the "methodical" killing of two dozen Iraqi civilians - including women and children - in what may be the worst incident of its kind since the 2003 invasion.
The Pentagon had said initially that the Iraqis were killed by an insurgent bomb and a separate inquiry is investigating whether there was a cover-up.
Results of the Naval Criminal Investigation Service's (NCIS) inquiry have not been published but officials briefed on the matter said not one civilian had been killed as the result of a makeshift bomb and that the marines had not come under hostile fire.
The killings took place in November in Haditha, a city north-west of Baghdad considered an insurgent stronghold. When reports of the deaths first emerged the Pentagon said one marine and 15 civilians were killed by a roadside bomb.
It now appears a marine was killed by the bomb and that his colleagues then moved through the area, shooting five men standing next to a taxi and then entering at least two homes containing women and children where the killings continued.
"This was not a burst of fire but a sustained operation over several hours, maybe five hours," one official told The New York Times.
The military was forced to investigate the issue after a video recording, made by a young survivor of the incident and provided to Time magazine, suggested something very different to the official story had taken place.
Three United States Marines officers have been relieved of their duties while inquiries continue.
Peace campaigners said yesterday that the inquiry's conclusion raised the prospect that other incidents reported to have involved the killing of "insurgents" actually involved the death of civilians.
Andrew Murray, the chairman of the Stop the War Coalition, said: "It's clear that what happened in Haditha is a war crime. By any measure it would be idle to think this is the first war crime that has been committed in the last three years during the occupation of Iraq. It must be assumed that more of this is going on."
Jeff Leys, a spokesman for the US-based anti-war group Voices in the Wilderness, said when he was in Iraq he had learnt about the deaths of civilians in disputed circumstances that he was now having to reconsider. "It seriously raises the question in my mind," he said.
The killings in Haditha are just the latest of several such incidents to be investigated by the military. Marines are also under investigation for killings earlier this year in Fallujah. Last year the military decided not to pursue charges against a marine who shot dead an unarmed insurgent in Fallujah in November 2004 - an incident filmed by an NBC cameraman.
The Pentagon has refused to comment on the investigation's findings, saying the inquiry was ongoing. Earlier this week the Marine Corps commandant, General Michael Hagee flew to Iraq to address troops, apparently out of concern about the inquiry's findings.
"Many of our marines have been involved in life-or-death combat or have witnessed the loss of their fellow marines, and the effects of these events can be numbing," he said in a statement. "There is the risk of becoming indifferent to the loss of a human life, as well as bringing dishonour upon ourselves."
The Pentagon says it does not keep records of the numbers of civilians killed in Iraq. A study published 18 months ago in The Lancet medical journal suggested more than 100,000 could have been killed. General Tommy Franks, the US commander during the invasion, notoriously said: "We don't do body counts."
Many veterans have talked about the brutalising effects of the war. Hart Viges, who was in the 82nd Airborne Division and saw action in Baghdad and Fallujah, said troops were forced into impossible situations. He even witnessed an order to open fire on all taxis in the city of Samawa because it was believed Iraqi forces were using them. He still suffers nightmares: "You can't wash your hands when they're covered in blood. The wounds carry on. This is what war does to your soul, to your humanity."
Another veteran, Specialist Jody Casey, told the BBC his unit was advised to carry shovels in their vehicles which they could plant on civilian victims to make it look as if they were concealing roadside bombs.
"I have seen innocent people being killed. IEDs [improvised explosive devices] go off and [you] just zap any farmer that is close to you," he said. "You're driving down the road at three in the morning. There's a guy on the side of the road, you shoot him ... you throw a shovel off."Reuse content