In one of the most deadly friendly-fire cases in more than a decade, five U.S. Special Operations troops and at least one Afghan soldier were killed accidentally by an airstrike in southern Afghanistan. American and Afghan officials said the incident took place Monday night in Zabul province, where Afghan troops were conducting security operations. When they were ambushed by Taliban fighters, they called for air support. Instead, the aircraft accidentally struck the location of the U.S. soldiers, killing five of them and at least one Afghan soldier. Since the war began, there have been more than a dozen instances of airstrikes or accidental firing on allies and fellow coalition troops, the most famous resulting in the death of NFL player Pat Tillman in 2004.