Coalition officials say an individual wearing an Afghan Army uniform shot and killed three U.S. troops in eastern Afghanistan Saturday.
Other soldiers in the area quickly killed the assailant, the officials said.
The three U.S. troops served in Army Special Operation Forces and were taking part in a training exercise when the assailant turned the gun on them.
It's unclear whether the gunman was actually part of the Afghan Army or had stolen the uniform.
Similar, so-called "green on blue" attacks killed dozens of coalition soldiers last year.