A NATO airstrike killed four guards working for a private security company in southern Afghan province of Helmand, officials said Wednesday.
One more guard was injured in the strike in Gerishk district on Tuesday, said Mohammad Hakim Andar, provincial police chief. The men were providing security for a road construction firm in the region, he said, DPA reported.
Major Michael Johnson, spokesman for the NATO-led International Security Assistance Force (ISAF), said a joint investigation with Afghan officials was underway into incident.
The military engaged a group of suspected militants in the area after an ISAF ground patrol was attacked, Johnson said.
"Following the engagement we heard allegations that four security guards were killed," he said.
"Friendly fire" casualties are not rare in southern Afghanistan. where the militants often operate in the vicinity of local forces.
Taliban are still most active in Helmand and neighbouring Kandahar, despite a reduction in their presence after major operations by NATO forces in the region last year.