Two coalition service members, an Afghan police officer and one civilian were killed in western Afghanistan on Wednesday when a mentoring session turned into a shootout, military officials said.
Officials with NATO's International Security Assistance Force were trying to determine what caused the shooting.
The shooting apparently happened during a mentoring session between coalition soldiers and the Afghan national police, coalition officials said in a statement.
During the mentoring session, an Afghan officer began firing a gun and the coalition soldiers returned fire, the statement said.
The incident, which occurred in the Badghis province, was followed by a demonstration by locals in the area, according to the statement.