A US helicopter attacked two Kurdish police outposts Sunday, killing four policemen and wounding eight others, a Kurdish security official said. The US military said it was investigating the report. Jabar Yawer, spokesman for the Kurdish Peshmerga militia, said the attack occurred about 10 a.m. on two small police outposts on a road linking Qara Tepe and Sadiya, about 110 kilometers northeast of Baghdad. He said two police vehicles also were destroyed and he believed the attack was mistaken friendly fire. The Kurdish Interior Minister issued a statement demanding an explanation for the attack. "We demand American troops to give an explanation for the US airstrike against a police station. The US troops should take care to understand what troops are deployed in the border areas."