The U.S. military says one of its service members was killed by "enemy small-arms fire" in Afghanistan on January 22.
The incident was under investigation, a statement said, without providing further details.
It did not name the service member or the branch of the military, pending notification of the family.
News of the death came the day after a suicide bombing attack by the Taliban on an Afghan military base in the eastern Afghan province of Maidan Wardak killed dozens of members of the Afghan security forces.
Some 14,000 U.S. soldiers are currently serving in Afghanistan, where the United States and NATO formally concluded their combat mission in 2014.
Most of the remaining Western forces in the country primarily train and advise local security forces, which have been struggling against attacks from a resurgent Taliban and other militant extremist groups.