Allegations that a NATO attack killed 24 Pakistani soldiers near the Afghan border Saturday dealt a serious blow to already tense relations between Washington and Islamabad at a time when the U.S. needs Pakistan's cooperation in engineering a peaceful resolution to the 10-year war in Afghanistan.
If confirmed, the NATO helicopter and fighter jet attack would be the deadliest ever involving Pakistani security forces.
In response, Pakistan shut down crucial border crossings used by convoys delivering supplies to NATO forces in Afghanistan and gave the U.S. 15 days to vacate an air base in southern Pakistan that in the past had been suspected as a launchpad for CIA drone attacks.
Local officials said the incursion occurred about 2 a.m. Saturday at two Pakistani army posts in Salala, a border village in the restive northwestern tribal region of Mohmand. Two of the dead were a captain and a major, said the officials, who spoke on the condition of anonymity because they were not authorized to speak on such matters.
The rugged Pakistan-Afghanistan border is extremely porous and difficult to police, enabling Afghan Taliban insurgents enjoying sanctuary in Pakistan to attack U.S. and Afghan forces in Afghanistan, and for Pakistani Taliban militants on the Afghan side of the border to attack Pakistani troops and posts.
In previous incidents involving NATO aircraft fire on Pakistani security forces, North Atlantic Treaty Organization officials have said their troops were either pursuing Taliban militants or thought they were shooting at insurgents.
NATO spokesman Brig. Gen. Carsten Jacobson said it was "highly likely" that alliance aircraft caused the deaths. He told the BBC that close air support had been called in when "a tactical situation developed on the ground," but gave no further details.
U.S. Gen. John Allen, commander of U.S. and NATO forces in Afghanistan, said the incident was being investigated. "This incident has my highest personal attention and my commitment to thoroughly investigate it to determine the facts," Allen said in a statement.
Although Pakistan tacitly permits the U.S. to carry out drone missile strikes against militant compounds and vehicles in the country's tribal areas, it has adamantly emphasized that it would not allow airstrikes or ground incursions on its territory.
U.S. military officials, however, have stated that their rules of engagement allow NATO aircraft to act in self-defense against insurgents who have launched attacks against NATO or Afghan forces from Pakistani territory. The U.S. has previously said that Pakistan abided by those rules, though Pakistani officials say no such accord exists.
Pakistani authorities said Saturday's assault was unprovoked and denounced it as a gross violation of their country's sovereignty. Army Chief of Staff Gen. Ashfaq Parvez Kayani condemned the attack as "a blatant and unacceptable act." The military said it had lodged a protest with NATO and coalition forces in Afghanistan, demanding that "strong and urgent action be taken [against] those responsible for this aggression."
The military said the attack involved both NATO helicopters and fighter aircraft, and that Pakistani troops fired back at the aircraft. At least 13 soldiers were injured, according to a statement released by the Pakistani military.
Pakistan's Foreign Ministry said in a statement that the attack was "a serious transgression of oft-conveyed red lines and could have serious repercussions" for Pakistan's cooperation with U.S. and NATO forces in Afghanistan.
Pakistani officials at the Torkham checkpoint at the Khyber Pass said Saturday afternoon that they had suspended all movement of NATO tankers and supply trucks heading into Afghanistan. A second border crossing in the southern town of Chaman also was shut down.
A similar incident occurred more than a year ago, when NATO helicopters crossed into Pakistan's Kurram tribal region along the Afghan border and fired on paramilitary troops at a border patrol checkpoint, killing two Pakistani soldiers. The U.S. government and NATO formally apologized for the deaths of the soldiers, saying the helicopter crews mistook the men for insurgents.
At the time, Pakistan responded to the incident by closing the Torkham checkpoint for 11 days, if effect stopping the movement of trucks and tankers ferrying fuel and supplies to NATO troops in Afghanistan. The border shutdown created a massive bottleneck, which paved the way for a series of militant attacks on parked NATO oil tankers and trucks across Pakistan. More than 150 NATO trucks were set ablaze or damaged and at least six people were killed in those attacks.
Pakistan plays a key role in keeping supply lines open for U.S. and Western troops battling Taliban insurgents in Afghanistan, which also gives Islamabad leverage when angered by Washington. About 40% of NATO's nonlethal supplies bound for Afghanistan move by truck from the Pakistani port city of Karachi to either the northwest border crossing at Torkham or the southern crossing at Chaman.
The Mohmand incident could have deeper fallout if it jeopardizes Pakistan's willingness to cooperate with Washington's push for a negotiated end to the war in Afghanistan. Although the U.S. no longer expects Pakistan to uproot the deadly Afghan Taliban affiliate known as the Haqqani network from Pakistani territory, it still wants Islamabad to help persuade Haqqani leaders to participate in peace talks.
"The confidence that was already lacking in the relationship will further take a deep, downward trend," said security analyst Talat Masood, a retired Pakistani general. "The public will react very adversely to this incident. The military cannot possibly continue to cooperate unless they know exactly what has happened. They need to know the American version of this as soon as possible."
The strike comes at an especially low point in U.S.-Pakistani relations. The U.S. raid into Pakistan that killed Osama bin Laden this year revealed the profound lack of trust between the two countries. More recently, the Pakistani ambassador to the U.S. was pushed to resign because he was accused of sending an unsigned letter soon after the raid to Adm. Michael G. Mullen, former chairman of the Joint Chiefs of Staff, pleading for American help in preventing a possible coup in the wake of the Bin Laden raid.
"The context is much more volatile than when this happened a few years ago," said Brian Fishman, counter-terrorism research fellow at the New America Foundation. "It's very dangerous now because you can get in a situation where especially in Pakistan, people might feel like they will have to take a very strong stand against the U.S. and NATO."
Times staff writers Laura King in Kabul, Afghanistan, and Neela Banerjee in Washington and special correspondent Zulfiqar Ali in Peshawar, Pakistan, contributed to this report.