NATO officials said Tuesday's shooting occurred in Wardak province west of Kabul, The New York Times reported. Coalition officials did not identify the nationality of the troops.
Shahidullah Shahid, a spokesman for Wardak's governor, said the man entered a small NATO base near a village then opened fire on U.S. soldiers.
Khaama Press said the gunman was a person wearing an Afghan uniform; the Times said the man was an Afghan soldier.
Tuesday's attack happened two days after three British soldiers were killed by a member of the Afghan police force in Helmand province. Afghan soldiers and police officers have attacked U.S. and other coalition troops with greater frequency as the international forces prepare to withdraw from the country and have been training Afghans to fight on their own.