New crisis for US-Pakistani ties
The 26 November strike by Nato forces on a Pakistani border post, which the Pakistani army says killed 25 soldiers, marks a new low in the troubled relations between Pakistan and the United States.
Analysts say the Pakistani response has been tough - the government has suspended Nato supplies passing through Pakistan and has given the Americans a deadline to vacate an airbase in the southwest of the country.
Pakistan has also indicated a review of diplomatic, political, military and intelligence ties with the US, and with Nato and Isaf forces in Afghanistan.
Top American officials have done some fire-fighting to salvage a relationship which they say is important to their efforts to restore peace to South Asia, and to Afghanistan in particular.
In a joint statement on Saturday the US foreign and defence secretaries offered their condolences to the Pakistan's leadership.
Late on Saturday night, US Secretary of State Hillary Clinton, Defence Secretary Leon Panetta and the commander of the Nato-led troops in Afghanistan, General John Allen, also made personal phone calls to their Pakistani counterparts to express their sympathy.
There has not yet been any official Pakistani reaction to the phone calls, nor to the joint statement.
Dr Hasan Askari Rizvi, a defence analyst based in Lahore, says that both countries need each other and will do their best to resolve the latest crisis. But attacks like this are making Pakistan's job of cooperating with the US more difficult.
"In the atmosphere of widespread anti-Americanism that prevails in the country, the only forces that have maintained a working relationship with the US are the Pakistani army, the ruling Pakistan Peoples Party, and its two main political allies, the ANP and MQM parties," says Dr Rizvi.
"Each time there is an attack against Pakistani installations, the credibility of these forces is undermined, reducing their ability to pacify public opinion and to defend cooperation with the US," he adds.
The US and Pakistan desperately need each other in order to shape the future of a stable and neutral Afghanistan before Western combat troops withdraw next year.
But whether they can do so will largely depend on how the two resolve this latest crisis.
Keeping the door open
Pakistan's move to "indefinitely" suspend Nato supplies through Pakistan is a harsh measure, but not unprecedented.
In September 2010, when shelling by Nato helicopters killed two Pakistani border guards in the Kurram tribal region, supplies were suspended for 11 days - one of a number of occasion when supplies have been stopped.
In the Kurram incident, supplies were resumed after US officials apologised for the attack.
Officials estimate that more than 40% of Nato's non-lethal supplies pass through Pakistan.
Previously, the Americans have sought to develop an alternative supply route through Central Asia to avoid these repeated disruptions.
It is more tortuous and expensive as it passes through several countries before reaching Afghanistan, but it is workable.
Pakistanis are aware of this, and of the fact that a permanent closure of the Pakistani route could dent Pakistan's leverage in Afghan affairs more than it might hurt the operational capabilities of Nato.
Perhaps because of this, when the defence committee of the Pakistani cabinet held an emergency meeting on Saturday following the Nato attack, it opted for "indefinite suspension" of supplies rather than their permanent termination, which had also been suggested at the meeting.
The Pakistanis clearly want to keep the door to negotiations open.
The decision to order the Americans to vacate the Shamsi airbase in Balochistan province is also not new.
Pakistan had told the Americans to leave the base in March, following a diplomatic row over Raymond Davis, a CIA contractor who had shot and killed two Pakistanis in the eastern city of Lahore.
US officials said at the time that they had already removed combat troops from the airbase and only some technical staff were still stationed there, using the base for logistical purposes.
The base is leased to the government of the United Arab Emirates, who in turn allowed the Americans to use it following the 9/11 attacks in 2001.
It is not clear if the Pakistani government has contacted the UAE to order the expulsion of the remaining Americans from the base, or whether it has any plans to do so.
For many, this announcement is seen as more for public consumption, rather than as a measure which will truly dent the capabilities of Western forces in the region.
The government has indicated it will carry out a thorough review of its political, diplomatic, military and intelligence cooperation with the US and Nato, but there is no sign that the relevant authorities have been asked to start this process.
Pakistan does have the option to stop cooperating in the all-important process of negotiating a settlement of the Afghan crisis.
To that end, it could scale down its participation at a forthcoming conference in Bonn and refuse to bring the militant groups over which it has influence to the negotiating table.
For their part, the Americans have the option of making further cuts in military assistance to Pakistan, thereby damaging its capability.
The Pakistani military depends almost entirely on US defence production to maintain the bulk of its weapons systems which are of US origin.
While attacks like the one in Mohmand undermine the ability of pro-US forces in Pakistan to publicly justify their cooperation in the "war on terror", much will depend on how the US can provide those forces with a face-saving public gesture while at the same time keeping pressure on them behind the scenes to deliver results.