Afghan policeman kills U.S. soldier

Also, an airstrike by foreign troops in the southern province of Helmand killed several women and children, a provincial police chief said. Troops led by the North Atlantic Treaty Organization said in a statement that they were aware of an airstrike in Nad Ali district but were "unable to confirm any civilian casualties."

The officer standing on a tower attacked the American foot patrol returning to a base in the Bermel district of Paktika province in eastern Afghanistan, the U.S. military said. The troops returned fire, killing the policeman.

It was the second attack on U.S. soldiers by an Afghan policeman in less than a month. Militants have disguised themselves in police and army uniforms in the past when conducting attacks on Afghan and foreign troops, but the two incidents involved actual policemen.

Training of the Afghan police force and national army are key elements in the U.S. strategy of dealing with the Taliban-led insurgency that has spread in the country.

Last month, an officer opened fire on U.S. troops at a police station in Paktia province in eastern Afghanistan, killing an American soldier and wounding three other service members. U.S. forces then killed the policeman.

Both provinces border Pakistan and experience many clashes between U.S. troops and insurgents.