The U.S. military said on Monday it had accidentally killed nine Iraqi civilians, including a child, while pursuing al Qaeda fighters south of Baghdad.
Three other civilians, including two more children, were wounded in the incident on Saturday near Iskandariya, 40 km (25 miles) south of Baghdad. The wounded were taken to U.S. military hospitals for treatment.
"We offer our condolences to the families of those who were killed in the incident and we mourn the loss of innocent civilian life," the U.S. military said in a statement e-mailed to Reuters.
It said U.S. military commanders in the area met a tribal sheikh in the area after the incident.
No other details were immediately available from the military but Iraqi police said U.S. helicopters had fired on a checkpoint manned by a neighbourhood police patrol.
They said women were among the victims.
The New York Times newspaper reported on Monday that U.S. aircraft, responding to an attack on a military convoy, had mistakenly fired on the checkpoint.
The neighbourhood units, formed by mainly Sunni Arab tribal sheikhs, have been credited for contributing to sharp falls in violence across Iraq in the past few months.
Attacks across Iraq have fallen by 60 percent since last June, when an extra 30,000 U.S. troops became fully deployed.
The incident was one of the worst of its kind since last October, when as many as 11 civilians may have been killed in U.S. air strikes.
Critics say U.S. forces often call in strikes on targets, including buildings where militants are believed to be hiding, without taking reasonable care to find out who might be inside.
The U.S. military says militants often deliberately use civilians as shields against attacking U.S. forces.
