|Scores of Nato lorries have been torched since Pakistan closed a key border crossing into Afghanistan [AFP]
The US has apologised for a recent helicopter attack that killed two Pakistani soldiers at an outpost near the Afghan border, saying the American pilots mistook the soldiers for Taliban fighters they were pursuing.
Wednesday's apology, which came after a joint investigation with Pakistan, could pave the way for Islamabad to reopen a key border crossing that Nato uses to ship goods into landlocked Afghanistan.
Pakistan closed the crossing in apparent reaction to the September 30 incident.
Taliban fighters have taken advantage of the impasse to launch attacks against stranded or rerouted lorries, including two on Wednesday. A driver was killed and at least 55 fuel tankers were set on fire in the attacks.
"We extend our deepest apology to Pakistan and the families of the Frontier Scouts who were killed and injured," Anne Patterson, the US ambassador to Pakistan, said.
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, Major Fazlur Rehman, a spokesman for the Frontier Corps said.
Pakistani soldiers fired at the two US 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," Tim Zadalis, Nato's director for air plans in Afghanistan who led the investigation, said.
"This tragic event could have been avoided with better coalition force co-ordination with the Pakistan military."
Nato officials have insisted that neither the attacks on lorries nor the border closure have caused supply problems for Nato troops as hundreds of lorries 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 US and Pakistani officials have predicted Torkham would reopen soon, and the apologies issued on Wednesday could provide Pakistan with a face-saving way to back down.
Al Jazeera's Kamal Hyder, reporting from Islamabad, the Pakistani capital, said "it is very unusual that the US says sorry for such a strike".
"The US air strikes are not a small matter anymore in Pakistan.
"Many people believe there is a tacit agreement between the US and the Pakistan government about these air strikes. It will be interesting to see how the government in Islamabad will handle the pressure over the matter," he said.
Even if the border is reopened, underlying tensions will remain in the US-Pakistan relationship, especially over Pakistan's unwillingness to go after Afghan Taliban fighters on its territory.
In an assessment of operations in Pakistan's tribal areas, a White House report to congress said that Pakistani forces were avoiding "direct conflict" with the Afghan Taliban annd al-Qaeda.
It also said that the Pakistani military has moved against fighters in South Waziristan, but that soldiers stayed close to roads and operations were progressing "slowly".
"In my mind, there's no question that the Pakistanis walk both sides of the street," Dianne Feinstein, the chairwoman of the Senate Select Committee on Intelligence, said.
The US has dramatically increasing the number of CIA drone strikes in Pakistan's tribal belt, including two on Wednesday that killed 11 fighters in North Waziristan, according to Pakistani intelligence officials.
In the first attack, a US drone fired two missiles at a house near Miran Shah, the main town in North Waziristan, killing six fighters, said the officials.
About two hours later, missiles struck a house near Mir Ali, another major town in North Waziristan, killing five fighters, they said.
The US does not publicly acknowledge the drone strikes in Pakistan, but US officials have said privately that they have killed several senior Taliban and al-Qaeda commanders.
Pakistani authorities reported 24 attacks since September 3 which have killed more than 140 people.