The NATO-led force in Afghanistan says three of its troops were killed Saturday when a man wearing an Afghan security forces uniform shot them.
Afghan officials confirmed the incident, saying the attack took place in the eastern province of Paktia.
So-called "insider attacks," when Afghan forces turn their guns on their foreign partners, have killed large numbers of foreign soldiers in Afghanistan.
The attacks come as foreign forces are training the Afghans to take over the nation's security, ahead of NATO's withdrawal next year.
In a statement, NATO said it is working with Afghan officials to assess Saturday's incident.
In line with NATO policy, the statement did not give the victims' nationalities.
Some information for this report was provided by AP, AFP and Reuters.