Khalaf, a 33-year-old security officer guarding oil pipelines, saw a US helicopter land near his home. American soldiers stormed out of the Chinook and advanced on a house owned by Khalaf’s brother Fayez, firing as they went.

Khalaf ran from his own house and hid in a nearby grove of trees. He saw the soldiers enter his brother’s home and then heard the sound of women and children screaming.

“Then there was a lot of machinegun fire,” he said last week. After that there was the most frightening sound of all — silence, followed by explosions as the soldiers left the house.

Once the troops were gone, Khalaf and his fellow villagers began a frantic search through the ruins of his brother’s home. Abu Sifa was about to join a lengthening list of Iraqi communities claiming to have suffered from American atrocities.

According to Iraqi police, 11 bodies were pulled from the wreckage of the house, among them four women and five children aged between six months and five years. An official police report obtained by a US reporter for Knight Ridder newspapers said: “The American forces gathered the family members in one room and executed 11 people.”

The Abu Sifa deaths on March 15 were first reported last weekend on the day that Time magazine published the results of a 10-week investigation into an incident last November when US marines killed 15 civilians in their homes in the western Iraqi town of Haditha.

The two incidents are being investigated by US authorities, but persistent eyewitness accounts of rampaging attacks by American troops are fuelling human rights activists’ concerns that Pentagon commanders are failing to curb military excesses in Iraq.

The Pentagon claims to have investigated at least 600 cases of alleged abuse by American soldiers in Iraq and Afghanistan, and to have disciplined or punished 230 soldiers for improper behaviour. But a study by three New York-based human rights groups, due to be published next month, will claim that most soldiers found guilty of abuse received only “administrative” discipline such as loss of rank or pay, confinement to base or periods of extra duty.

Of the 76 courts martial that the Pentagon is believed to have initiated, only a handful are known to have resulted in jail sentences of more than a year — notably including the architects of detainee abuse at Abu Ghraib prison.

Most other cases ended with sentences of two, three or four months. “That’s not punishment, and that’s the problem,” said John Sifton of Human Rights Watch, which is compiling the study with two other groups.

“Our concern is that abuses in the field are not being robustly investigated and prosecuted, and that they are not setting an example with people who cross the line,” said Sifton. “There is a clear preference by the military for discipline with administrative and non-judicial punishments instead of courts martial. That sends the message that you can commit abuse and get away with it.”

Yet the evidence from Haditha and Abu Sifa last week suggested that the Pentagon is finding it increasingly difficult to dismiss allegations of violent excesses as propaganda by terrorist sympathisers.

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