The desert's nighttime chill had taken hold at a small U.S.-Afghan base in the Taliban's heartland: the home village, in fact, of Mullah Mohammed Omar, the movement's founder and supreme commander. For the American troops manning the outpost, though, the danger came not from outside the wire, but from within.

Hours before dawn Thursday, Afghan assailants, including a man hired to teach Afghan soldiers to read, shot and killed two U.S. troops and wounded a third, Afghan and American officials said. The soldiers slain at the base in Kandahar province were the fifth and sixth U.S. military personnel to die in a span of eight days at the hands of Afghans they had worked alongside.