Three American and three NATO troops were shot and killed by Afghans Friday in separate attacks in Helmand province.
The U.S. Department of Defense said an Afghan police officer killed three American special forces marines Friday morning.
On Friday night, three NATO troops were gunned down by an Afghan working on a shared installation.
Their nationality hasn't been released.
The attacks were a day after a suicide bomber killed four Americans in eastern Afghanistan.
This also marks the third attack this week on coalition soldiers by Afghans in military uniforms.