The Defense Department says the three troops killed Saturday in eastern Afghanistan by an Afghan wearing a security forces uniform are Americans.
It appears to be the seventh such attack by a member of the Afghan forces against their international allies.
A Defense Department official says no details will be released about the three American troops killed in the attack until after notification of relatives.
An Afghan Defense Ministry spokesman says the shooting took place Saturday near the Pakistan border in the capital of eastern Paktia province, the city of Gardez. A security official there says the attack took place inside a base of the Afghan army in Gardez.
So far this year, 11 foreign soldiers have been killed in such attacks, including the attack Saturday.