IT was an “isolated incident”, US officials insisted. The murder of 16 Afghan civilians as they slept, Hillary Clinton declared, was the “inexplicable act” of one soldier.

And as Barack Obama and David Cameron prepared to put a public gloss on an earlier end to Nato’s “lead combat” mission in Afghanistan, the US secretary of state pledged to continue “protecting the Afghan people”.

After a decade of ever more degraded Nato occupation, who could conceivably wish for such protection? The slaughter of innocents in Panjwai, nine of them children, follows the eruption of killings and protests after US troops burned copies of the Quran last month. That came soon after the exposure of video of US marines urinating on dead Afghans.

The evidence surrounding the Panjwai massacre is so far contradictory. If it was the work of a single gunman, he was presumably unhinged or motivated by perverted religious or racist hatred. But however extreme, it was certainly not an isolated incident.

As in Iraq, the killing and abuse of civilians by occupation forces has been an integral part of this dirty war from its earliest days. As it drags on, ever more outrages emerge. Last year, members of a US unit were convicted of killing Afghan civilians for entertainment, cutting off body parts as trophies and leaving weapons with the corpses to make it seem as if they were killed in combat.

Nor is such depravity just a US habit, of course. Last year a hungover British guardsman stabbed a 10-year-old boy in the kidneys for no reason. British soldiers are currently on trial for filming their abuse of Afghan children, while US WikiLeaks files record 21 separate incidents of British troops shooting dead or bombing Afghan civilians.

The line between deliberate and accidental killings is in any case a blurred one. As Gen Stanley McChrystal commented: “We have shot an amazing number of people, but to my knowledge, none has ever proven to be a threat.” — The Guardian, London