The incident occurred on Route 9, near Najaf, when a car carrying 13 women and children approached a checkpoint.
A US military spokesman says the soldiers motioned the vehicle to stop but their signals were ignored. However, according to the Washington Post, Captain Ronny Johnson, who was in charge of the checkpoint, blamed his own troops for ignoring orders to fire a warning shot.
"You just [expletive] killed a family because you didn't fire a warning shot soon enough!", he reportedly yelled at them.
In another checkpoint incident this morning, US forces say they killed an unarmed Iraqi driver outside Shatra.
Meanwhile it has emerged - as a result of detective work on the internet by a Guardian reader - that the explosion in a Baghdad market which killed more than 60 people last Friday was indeed caused by a cruise missile and not an Iraqi anti-aircraft rocket as the US has suggested.
A metal fragment found at the scene by British journalist Robert Fisk carried various markings, including "MFR 96214 09". This, our reader pointed out in an email, is a manufacturer's identification number known as a "cage code".
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