ISLAMABAD -- The U.S. apologized for a recent helicopter attack that killed two Pakistani soldiers at an outpost near the Afghan border, saying American pilots mistook the soldiers for insurgents they were pursuing.
Wednesday's apology, which came after a joint investigation, could pave the way for Pakistan to reopen a key border crossing that NATO uses to ship goods into landlocked Afghanistan. Pakistan closed the crossing to NATO supply convoys in apparent reaction to the Sept. 30 incident.
Suspected militants have taken advantage of the impasse to launch attacks against stranded or rerouted trucks, including two Wednesday where gunmen torched at least 55 fuel tankers and killed a driver.
"We extend our deepest apology to Pakistan and the families of the Frontier Scouts who were killed and injured," said the U.S. ambassador to Pakistan, Anne Patterson.
Pakistan initially reported that three soldiers were killed and three wounded in the attack, but one of the soldiers who was critically injured and initially reported dead ended up surviving, said Maj. Fazlur Rehman, the spokesman for the Frontier Corps.
Pakistani soldiers fired at the two U.S. helicopters prior to the attack, a move the investigation team said was likely meant to notify the aircraft of their presence after they passed into Pakistani airspace several times.
"We believe the Pakistani border guard was simply firing warning shots after hearing the nearby engagement and hearing the helicopters flying nearby," said U.S. Air Force Brig. Gen. Tim Zadalis, NATO's director for air plans in Afghanistan who led the investigation. "This tragic event could have been avoided with better coalition force coordination with the Pakistan military."
The head of U.S. and NATO forces in Afghanistan, Gen. David Petraeus, also expressed his condolences, saying in a statement that "we deeply regret this tragic loss of life and will continue to work with the Pakistan military and government to ensure this doesn't happen again."
Pakistan moved swiftly after the attack to close the Torkham border crossing that connects northwestern Pakistan with Afghanistan through the famed Khyber Pass. The closure has left hundreds of trucks stranded alongside the country's highways and bottlenecked traffic heading to the one route into Afghanistan from the south that has remained open.
There have been seven attacks on NATO supply convoys since Pakistan closed Torkham, including those Wednesday.
NATO officials have insisted that neither the attacks nor the border closure have caused supply problems for NATO troops since hundreds of trucks still cross into Afghanistan each day through the Chaman crossing in southwestern Pakistan and via Central Asian states.
But reopening Torkham is definitely a priority for NATO because it is the main crossing in Pakistan, the country through which NATO ships the majority of its supplies into Afghanistan. Other routes are more expensive and logistically difficult.
Both U.S. and Pakistani officials have predicted Torkham would reopen soon, and the apologies issued Wednesday could provide Pakistan with a face-saving way to back down.
Reopening the border could reduce the frequency with which militants have attacked NATO supply convoys in recent days, although such attacks occurred regularly even before Torkham was closed.
The first attack Wednesday came early in the morning when an unidentified number of gunmen in two vehicles attacked trucks as they sat in the parking lot of a roadside hotel on the outskirts of Quetta, the capital of Baluchistan province. They were making their way to the Chaman crossing.
One driver was killed in the attack and at least 25 trucks were destroyed by fire that spread quickly from vehicle to vehicle, senior police official Hamid Shakil said.
On Wednesday night, suspected militants armed with assault rifles opened fire on oil tankers parked along the road in Khyber Pakhtunkhwa province as they were making their way to Torkham. At least 30 tankers were engulfed in flames, said local police officer Nisar Khan. It was unclear if there were any casualties.
Of the seven attacks on convoys bringing supplies in from the port city of Karachi since the Torkham closure, five were on trucks heading to that crossing and two were on their way to Chaman.
The convoys bring fuel, military vehicles, spare parts, clothing and other non-lethal supplies for foreign troops in Afghanistan.
It was unclear who was behind the latest attacks, but the Pakistani Taliban have claimed responsibility for similar assaults on NATO supplies.
The helicopter attack and the border closure have exposed the frequent strains in the alliance between Pakistan and the United States. But Pentagon spokesman Geoff Morrell downplayed the possibility of any lasting effects.
"There are incidents which create misunderstandings, there are setbacks, but that does not mean the relationship -- this crucial relationship to us -- is in any way derailed," Morrell said Tuesday.
Even if the border is reopened, underlying tensions will remain in the U.S.-Pakistan relationship, especially over Pakistan's unwillingness to go after Afghan Taliban militants on its territory with whom it has strong historical ties and who generally focus their attacks on Western troops, not Pakistani targets.
The U.S. has responded by dramatically increasing the number of CIA drone strikes in Pakistan's tribal belt, including two Wednesday that killed 11 militants in North Waziristan, according to Pakistani intelligence officials speaking on condition of anonymity because they were not authorized to talk to the media.
In the first attack, a U.S. drone fired two missiles at a house near Miran Shah, the main town in North Waziristan, killing six militants, said the officials.
About two hours later, missiles struck a house near Mir Ali, another major town in North Waziristan, killing five militants, said the officials.
The U.S. does not publicly acknowledge the drone strikes in Pakistan, but U.S. officials have said privately that they have killed several senior Taliban and al-Qaida commanders.