NATO officials say a person wearing an Afghan National Army uniform turned on coalition forces Wednesday and killed three servicemen.
A statement says the incident, which took place in southern Afghanistan, is under investigation.
The victims will be identified by the relevant national authorities.
International coalition servicemen in Afghanistan are frequently targeted by Taliban militants.
Earlier this month, a person wearing an Afghan police uniform shot and killed another coalition service member.
About 40 of coalition members have been killed in similar attacks this year.