A US airstrike struck checkpoints manned by US-allied Sunni fighters north of Baghdad on Saturday, killing six guards and wounding two, Iraqi police said. Meanwhile, three US soldiers were killed in a roadside bombing, the military said, bringing the American death toll since the war's start five years ago closer to 4,000. Two Iraqi civilians also were killed in the attack northwest of Baghdad. The military did not immediately respond to a request for comment on the reported friendly fire incident in Samarra. A police officer, speaking on condition of anonymity because he wasn't authorized to release the information, said the six members of the so-called awakening council were killed and two others were wounded when an airstrike hit two checkpoints about 100 meters (yards) apart.