"A more troubling explanation would be that insurgents in the area were operating under the nose of Pakistani security forces." It could be a tragic accident, but unfortunately, there is also ample precedent for such allegations.
An attack by Nato aircraft on Pakistani troops that allegedly killed as many as 28 soldiers and looks set to further poison relations between the US and Pakistan was an act of self-defence, a senior western official has claimed.
According to the Kabul-based official, a joint US-Afghan force operating in the mountainous Afghan frontier province of Kunar was the first to come under attack in the early hours of Saturday morning, forcing them to return fire.
The high death toll from an incident between two supposed allies suggests Nato helicopters and jets strafed Pakistani positions with heavy weapons.
The deadliest friendly fire incident since the start of the decade-long war also prompted Pakistan to ban Nato supply trucks from crossing into Afghanistan and to issue an order demanding the US quit the remote Shamsi airbase, from which the US has operated some unmanned drone aircraft.
A spokesman for Nato's International Security Assistance Force (ISAF) said it was "highly likely" that aircraft which had been called into the area to provide "close air support" to troops on the ground was responsible for causing casualties among the Pakistani soldiers.
For their part, a statement by the Pakistani military claimed that it was they who were attacked first, forcing them to respond to Nato's "aggression with all available weapons".
According to Pakistani officials the 40 or so soldiers stationed at the outposts were asleep at the time of the attack. Government officials said the two border posts that were attacked had recently been established to try to stop insurgents who use bases in Afghanistan to attack Pakistan from crossing the border and launching attacks.
Afghan intelligence say the US-Afghan force was conducting operations against suspected Taliban training camps in the area.
The vagueness of the border between Afghanistan and Pakistan is one potential, and relatively innocent, explanation for the incident. Drawn up by the British Raj in 1893, there is little agreement on where the so-called Durand Line actually falls, meaning troops from either side of the border can wander into the neighbouring country without realising it. One senior military official said that, in places, rival maps have discrepancies of "multiples of kilometres – sometimes as much as five kilometres".
Much of the fighting in Afghanistan is conducted by guerrillas based a short distance inside Pakistan. Nato forces are not allowed to cross the border and militants sometimes fire artillery and rockets across the line from locations close to Pakistani army posts.
And yet both sides have worked hard to try and minimise any confusion. The attack happened just a day after John Allen, the US commander of Nato forces in Afghanistan, met with Ashfaq Pervez Kayani, the Pakistani army chief, to discuss enhanced co-operation on the border.
But a more troubling explanation would be that insurgents in the area were operating under the nose of Pakistani security forces. Many Afghan officials believe Pakistan helps the Taliban with cross-border operations.
Edrees Momand of the Afghan Border Police said that a US-Afghan force in the area near the Pakistani outposts detained several militants on Saturday morning.
"I am not aware of the casualties on the other side of the border but those we have detained aren't Afghan Taliban," he said, implying they may have been Pakistani or other foreign national Taliban operating in Afghanistan....