KABUL, Afghanistan — An American soldier was killed Sunday afternoon when a man wearing an Afghan security force uniform opened fire on a group of foreign trainers in eastern Afghanistan, officials with the international military coalition said. It was the third such attack in less than a month. Connect With Us on Twitter Follow @nytimesworld for international breaking news and headlines. Twitter List: Reporters and Editors The shooting, which occurred in the Sharana district of Paktika Province, also most likely wounded at least one other soldier, but details about the extent of the damage were not immediately available. A spokesman for the…