Three U.S. contractors of the International Security Assistance Force (ISAF) where killed by an Afghan soldier in the province of Heart, official sources reported.
The event occurred on Sunday in Camp Zafar, one of the two camps where Afghan force are trained, located eight kilometers south the main base of the NATO-led troops in the province.
A communiqué released by the North Atlantic Treaty Organization (NATO) reported the event without specifying the place or the nationality of the Pentagon's contractors, but notes that the attacker died during the incident and underlines an investigation was set in motion.
However, spokesman of the province of Herat Muhaihuddin Nuri confirmed the media that the attack took place in a military training facility in that region and that those dead were Americans.
According to NATO, 20 attacks have taken place since January against foreign occupying troops. In 2011, 21 attacks were perpetrated killing 35 people.
Nearly 250 U.S. and ISAF people have died in this nation in so far 2012,