A person wearing an Afghan national security force uniform has turned his weapon against civilian contractors with the US-led military coalition, killing three.
In other incidents over the weekend, five NATO service members were killed in roadside bombings.
NATO said the attack on the civilian coalition workers occurred in western Afghanistan on Sunday but disclosed few other details.
The gunman was killed during the incident, which is still being investigated. No further information about the civilians who died was released.
Afghan security forces or militants dressed in their uniforms have been killing a rising number of coalition forces, but they have not been specifically targeting contractors working for the coalition. So far this year, 26 foreign troops have been killed in this type of attacks.