Five U.S. servicemembers and at least one Afghan soldier have been killed in what appears to be one of the deadliest instances of friendly fire of the war in Afghanistan. The soldiers were mistakenly killed by an airstrike that was called in by U.S. troops to beat back a Taliban ambush. The incident occurred in Zabul province where soldiers were conducting security operations ahead of Saturday’s presidential runoff. An earlier “friendly fire” strike killed five Afghan soldiers in March. Afghans have opposed the airstrikes for mistakenly killing civilians, with President Hamid Karzai refusing to sign a long-term security deal with the United States until the air attacks stop.