Reporting from Kabul, Afghanistan — The NATO force on Wednesday acknowledged that its helicopters strayed into Pakistani airspace and fired on a Pakistani border post last week, apparently after mistaking warning shots for hostile fire from insurgents.
The U.S. commander of Western troops in Afghanistan, Gen. David H. Petraeus, expressed regret and pledged to work with the Pakistani military and government "to ensure this doesn't happen again."
The Sept. 30 incident, in which two Pakistani soldiers were killed and four were wounded, sparked a furious reaction from Pakistan. It closed the main land crossing into Afghanistan, blocking convoys carrying NATO supplies.
Subsequently, insurgents mounted a series of fiery attacks on stranded trucks.
The findings were the result of a joint investigation by NATO and Pakistani authorities. Even with the Pakistani stamp of approval, and the apology from Petraeus, it was not clear whether it would cool angry public sentiment in Pakistan, where national sovereignty is an extremely sensitive issue.
The border incident occurred on the heels of a series of strikes by unmanned CIA drones targeting militant leaders holed up in Pakistan's tribal areas.
Those strikes appeared to be an indication that the United States had concluded that the Pakistani military would not take decisive action on its own against Al Qaeda, Taliban and other insurgent groups sheltering in Pakistan.
In its statement, the North Atlantic Treaty Organization appeared to be trying to differentiate the Sept. 30 strike from a deliberate helicopter pursuit the previous day in the volatile frontier region.
"The team concluded two coalition helicopters passed into Pakistan airspace several times," NATO's statement said. "Subsequently the helicopters fired on a building later identified as a Pakistan border outpost, in response to shots fired from the post."
The investigators concluded that it was "most probable" that soldiers manning the post were trying to warn the helicopter crews of their presence.
"Unfortunately, following the engagement, it was discovered that the dead and wounded were members of the Pakistan Frontier Scouts," the statement said.
Pakistan had initially said three of its troops were killed, but later revised that to two, saying one critically injured soldier had survived.
Air Force Brig. Gen. Tim Zadalis, the leader of the assessment team, said the event could have been avoided by better coordination with the Pakistan military.