The US military is investigating Iraqi police allegations that its soldiers shot dead a family of eleven in their home last week.
The inquiry comes a day after a magazine published allegations that Marines killed 15 civilians in another town last year. A criminal inquiry into those deaths was launched last week.
Time
magazine published accounts by townspeople saying troops went on a rampage after a Marine was killed by a roadside bomb in Haditha, west of Baghdad, in November.
The witnesses rejected an original US account that the 15 also died in the bomb blast.
"I watched them shoot my grandfather, first in the chest and then in the head," one child said. "Then they killed my granny."
The investigating is focusing on discrepancies between police and US army accounts of an incident in the town of Ishaqi, north of Baghdad, on Wednesday.
Police accused US troops of shooting dead eleven people, including five children, while the military said only four people were killed.
"Because of that discrepancy, we have opened an investigation," said spokesman Lieutenant-Colonel Barry Johnson.
Local police Colonel Farouq Hussein said autopsies had found that all the victims were shot in the head.
Accusations that US soldiers often kill civilians and that little disciplinary action has resulted in the few cases investigated have aroused Iraqi anger since the invasion.
In Duluiya - near Ishaqi - police on Sunday accused troops of killing a 13-year-old and his parents were among eight people killed. The US military said seven insurgents who attacked a patrol with rocket-propelled grenades were killed.
US military also officials confirmed that an account from Marines of the November killing of 15 civilians by a roadside bomb in Haditha was wrong and that the civilians were shot.
Time
magazine said this week that video tapes of the bodies it provided to the military in January had prompted the revision.