WHEN the news came through on November 26th that up to 24 Pakistani soldiers had been killed in a cross-border incident involving American and Afghan forces, your correspondent was at ISAF HQ in Kabul preparing to interview General John Allen, the commander of coalition forces in Afghanistan. The mood at ISAF was one of deep shock combined with a sense of foreboding. The timing was awful. General Allen had only just returned from a visit to General Ashfaq Parvez Kayani, chief of Pakistan's army general staff, in a bid to improve relations that were already under the severest strain. As well as closing the land corridor that provides ISAF with up to half of its supplies, Pakistan announced that it would boycott the following week's international conference in Bonn on the future of Afghanistan. The only (grim) smiles were caused by a reporter from a German news magazine who took a German general at ISAF to task for what he seemed to think was a deliberate attempt by America to sabotage his country's hosting of a successful conference.

Although the official line was to offer Pakistan condolences for the loss of life and to wait for the results of an official investigation before saying anything more, it was clear that there had been a major “screw up”. It wasn't just the lethality of what had occurred on the eastern border that was troubling—although it was the worst such “friendly fire” incident involving Pakistani forces in the ten years of the war—but the realisation that the air strikes had continued unabated for up to two hours. The release on December 22nd of the findings of the investigation largely bears out Pakistan's version of events. After coming under fire from the Mohmand tribal region on the other side of the border, the American and Afghan commandos called in air strikes, apparently confident that there were no Pakistani forces in the areas and that the strikes would be hitting insurgents. That was wrong. The mistake was further compounded when the Pakistani border control centre was given incorrect data about where the fighting was taking place. Whether either General Allen or America's defence secretary, Leon Panetta, will now issue the apology the Pakistanis have demanded is not yet certain. There is a precedent: Mr Panetta's predecessor, Robert Gates, apologised in 2010 after a similar incident.

Underlying the whole sorry story is the corrosive lack of trust between ISAF and Pakistan. ISAF is reluctant to tell Pakistani border forces precisely when and where it is carrying out operations against insurgents because it believes (with some justification) that the Taliban and their allies have in the past been tipped off by the Pakistanis when raids have been imminent. For their part, the insurgents often try to provoke incidents by launching attacks from positions near Pakistani troop positions. From Pakistan's point of view, its border guards, poorly-equipped and with little situational awareness, are innocent victims caught in the crossfire. The problem is only likely to get worse. After the security gains of the past 18 months in the south and west, particularly in Helmand and Kandahar provinces, the main focus of next year's fighting is likely to be in the still very violent east of Afghanistan, which borders the Pakistani tribal area of North Waziristan (where the formidable Haqqanis are based) and other lawless territories to the north. Unless ISAF and the Pakistanis can find a way of working better together, the potential for further bloody and politically destructive accidents will grow.