The deaths of 24 Pakistani troops spotlights the explosive 10-year war on the Afghan border, but is unlikely to rupture the unhappy marriage of convenience between Islamabad and Washington, analysts say. Forced into partnership by 9/11 and the war on al Qaeda, the two governments are totally reliant on one another, yet lurch from crisis to crisis given a prevailing climate of distrust.
It is typical that just as relations began to recover from the covert American raid that killed Osama bin Laden in May, the Nato attack has put the alliance back on the brink. Islamabad sealed the Afghan border to Nato supplies - a time-honoured response - again gave Americans notice to leave a shadowy air base believed to be used in the CIA drone war, and ordered a review of the alliance. But Islamabad and Washington have little wiggle room.
With Pakistan eyeing a general election by February 2013, the government cannot afford to be seen accepting the perceived breach of sovereignty, with the opposition only too happy to exploit a very real sense of anger. "I think we're one step short of a strategic crisis," retired US general turned NBC News military analyst Barry McCaffrey told the TV network.
Estimating that up to 50 percent of supplies for Afghanistan are routed through Pakistan he said: "we've got to talk to them, we've got to pay them, we've got to apologise for this strike. We have no option, literally." At the crux of the problem are accusations of complicity.
Afghan and US officers routinely complain that Pakistani soldiers do nothing to prevent Taliban opening fire from Pakistani soil or infiltrating the border - including in Mohmand, the district where the soldiers were killed. At other times, they accuse Pakistani troops of firing on their positions. Very often, Taliban, Afghan and Pakistani posts are very close to one another.
The border, disputed by ethnic Pashtuns living on both sides, is in many places unmarked and straddles some of the most hostile terrain in the world. "Insurgents repeatedly use the border area in their favour to hide, to operate across it and to fire on both sides," said Brigadier General Carsten Jacobson, spokesman for Nato's International Security Assistance Force.
Jacobson told AFP that Nato's mandate stopped at the Afghan border, but that troops can return fire in self-defence. US and Afghan commandos have reportedly strayed across the border in hot pursuit of Taliban. Although the working relationship between army chief Ashfaq Kayani and American top brass is considered to be relatively good, Pakistani analysts say there is a lack of co-ordination at operational levels.
Resolving the latest crisis will likely hinge on the outcome of a Nato investigation and to what extent Washington is willing to pacify a government in Islamabad answerable to a largely anti-American electorate. "Pakistan will surely want to know the exact motive of the attack. Was it the result of intelligence failure or a mistake by a group or an individual?" retired lieutenant general Talat Masood told AFP.
So will there be any lasting damage? To what extent can Pakistan force any change in its terms of engagement with the United States? "Long-term severing of ties is out of the question. Short-term retaliation is underway," said author Imtiaz Gul. Diplomats suggest that in addition to closing the border, Pakistan could restrict its airspace to the Americans and close off further logistic support. But the demand that American personnel leave Shamsi base within 15 days exposes only the limited options. Pakistan has frequently asked the Americans to leave the base and there were widespread reports earlier this year that US personnel had already done so.
The government is also widely understood to tacitly support the American drone war on Taliban militants who also pose a threat to its own security. "In the next few weeks, I think Pakistan may resume Nato supplies and the US will make certain commitments not to repeat such incidents," said Pakistan-based political analyst Hasan Askari.
But John Bolton, a former US ambassador to the United Nations, laid bare the dilemma for Washington in handling nuclear-armed Pakistan, which has received up to $20 billion in US aid over the last 10 years. "As long as that country has nuclear weapons that could fall into the hands of radicals and be a threat world-wide, they have incredible leverage," he said.