A witness told Reuters a suicide bomber wearing a police uniform struck as U.S. soldiers patrolled the city of Khost. A NATO spokeswoman confirmed only that the attack was carried out by a suicide bomber.
Provincial Governor Abdul Jabar Nahimi said the bomber had been riding a motorcycle packed with explosives and 37 civilians were wounded in the blast.
The Afghan Taliban claimed responsibility, although Afghan insurgents are quick to claim any successful attack on foreign troops as their own.
The bombing followed the killing of two Americans on Sunday in an exchange of fire with Afghan forces that took the death toll of U.S. military and civilian personnel to over 2,000 in the 11-year war.