The air raid destroyed one house, killing the 14 people inside, said the spokesman for the Joint Coordination Center, which handles information and liaises between U.S. and Iraqi forces.

Another four houses were hit and three people were injured in the raid on Monday night, he said.

"We have this information from the Iraqi police and army in Baiji," said the spokesman, who declined to give his name.

The U.S. military had no immediate comment.

Baiji has seen considerable rebel violence, including efforts by insurgents to disrupt oil and fuel flows through its refinery, the biggest in Iraq. The closure of the refinery last month is causing serious shortages in fuel across the country.

U.S. forces have used air power increasingly throughout the past year; official military data show only one strike was carried out in March and the average in the first quarter was five strikes per month compared to over 50 in the last quarter.

Iraqi medical staff, police and political leaders, particularly in the restive, Sunni Arab-dominated west and north, have reported civilian casualties in such raids; U.S. commanders say they make every effort to minimize that risk.