"One U.S. service member was killed and two other U.S. service members were wounded during an apparent insider attack in southern Afghanistan, July 7," said a statement from Resolute Support, the NATO-led military training mission in Afghanistan.
"The wounded service members, who are in stable condition, are currently being treated," said the statement. "The incident is under investigation."
The term "insider attack" refers to attacks carried out against U.S. military personnel by the Afghan troops they are training or advising.
The number of insider attacks peaked at 61 in 2012, but the attacks have become rare after the U.S. military instituted security safeguards to protect American troops.
The last insider attack occurred in August of 2017. In that incident, a Romanian soldier was injured.
There are about 14,000 U.S. military personnel in Afghanistan, most of them serving as trainers and advisers with the Afghan military in their fight against the Taliban and ISIS.
Army Specialist Gabriel Conde, 22, was killed by Taliban gunfire in a province east of the Afghan capital of Kabul on April 30.
Army Sgt. 1st Class Mihail Golin, 34, was killed in a firefight with ISIS fighters in eastern Afghanistan on January 1.