NATO forces say two American civilians and two Afghan soldiers have been killed in a shooting at a weapons training area in northern Afghanistan.

The international military coalition said in a statement that Tuesday’s shooting in Mazar—e—Sharif was apparently started by an Afghan army soldier who was a trainer at the base, Camp Shaheen. NATO says the soldiers were going through “routine weapons proficiency training” when the gunfire started. One of those killed was the alleged shooter.

One NATO service member and an Afghan soldier were wounded.

Afghan Defence Ministry spokesman Gen. Mohammad Zahir Azimi said an investigation had been launched into the incident.

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