WITH remarkable self-assurance for a ten-year-old girl, Iman Hassan recounted how her family was killed by American troops as she cowered in terror in a corner of her living room.

It happened soon after 7am on November 19 last year, she claimed in an interview with The Times. She was still in her pyjamas and preparing for school when a US military convoy rumbled down the road near her home in al-Haditha, a town on the Euphrates surrounded by date farms that has become a hotbed of insurgents. Three months earlier 20 American soldiers had been killed there.

At that moment a Humvee was blown up by a roadside bomb, killing Miguel Terrazas, its 20-year-old driver from El Paso, Texas. Iman’s father was praying in the next room of her house, a basic two-storey building made of breezeblocks. Her grandparents were still in bed. The family heard shots but knew to stay indoors.

What happened next is the subject of a massive inquiry by the US Naval Criminal Investigative Service. The results are expected to deal another devastating blow to America’s standing in Iraq and across the world.

US Congressmen briefed on the investigation expect it to conclude that Corporal Terrazas’s fellow marines ran amok, killing as many as 24 unarmed Iraqi civilians, including women and children, in cold blood. A dozen marines face courts martial or even charges of homicide. A separate inquiry is determining whether there was a cover-up.

Pentagon and military officials who have seen the findings of the investigation have said that it may be the worst case of misconduct by American ground forces in Iraq, and that includes the Abu Ghraib prisoner abuse. Critics will draw comparisons with the My Lai massacre during the Vietnam War, when US soldiers killed more than 500 unarmed villagers. Then it took 18 months for the truth to emerge, and changed the American public’s perception of the war.

The investigation is also coming to a head only days after President Bush and Tony Blair hailed the creation of Iraq’s new Government of national unity as a turning point in the country’s three-year descent into mayhem.

“It’s a disaster,” said Tareq al-Hashemi, Iraq’s Sunni Vice-President, who dislikes the occupation but does not want US troops to leave until the country is stable. “They are provoking all Iraqis, especially from the Arab Sunni community. They are pushing them to join the national resistance and to fight . . . Maybe some of them feel sympathetic to al-Qaeda now,” he told The Times.

“The situation in western Anbar province is out of control. This happened primarily because of the behaviour of the American Army — their large-scale violation of human rights. They are killing people, hurting people, destroying towns.”

As Iman tells it, US marines burst into her house 15 minutes after the bomb destroyed the Humvee, apparently looking for insurgents. They shouted at her father. Then a grenade was thrown into her grandparents’ room. She saw her mother hit by shrapnel. Her aunt grabbed a baby and ran from the house.

Soldiers opened fire inside the living room, where most of the family were gathered. Her uncle Rashid came downstairs, saw what was happening, then fled outside, where he was pursued by Marines and shot.

“Everybody who was in the house was killed by the Americans except my brother Abdul-Rahman and me,” Iman said. “We were too scared to move and tried to hide under a pillow. I was hit by shrapnel in my leg. For two hours we didn’t dare to move. My family didn’t die immediately. We could hear them groaning.”

Iman’s grandfather Abdul al-Hamid Hassan, her grandmother Khamisa, her father Walid, uncle Mujahid, her mother, uncle Rashid and cousin Abdullah, 4, had all been fatally wounded.

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