Media playback is unsupported on your device Media caption Pentagon spokesman George Little expressed the "deepest regret" for the loss of life

The US military has admitted it bears significant responsibility for last month's air strike on the Afghan border that killed 24 Pakistani soldiers.

A statement said US and Afghan troops acted in self defence, but conceded there had been a lack of proper co-ordination with Pakistani forces.

A Pentagon spokesman later expressed "deep regret" over the incident.

However, Pakistani army spokesman Maj Gen Athar Abbas dismissed the findings as "short on facts", Reuters reported.

In retaliation for the killings, Pakistan has closed its border with Afghanistan, cutting Nato supply lines.

Islamabad, a vital partner in the fight against militants in the region, has demanded a formal US apology.

'Incorrect mapping'

In the statement the US once again expressed its deepest regret for the "tragic loss of life" caused by the air strike in Mohmand tribal agency on 26 November.

"Inadequate co-ordination by US and Pakistani military officers operating through the border co-ordination centre - including our reliance on incorrect mapping information shared with the Pakistani liaison officer - resulted in a misunderstanding about the true location of Pakistani military units," it said.

We cannot operate effectively on the border... without addressing the fundamental trust still lacking between us US Department of Defense

"This, coupled with other gaps in information about the activities and placement of units from both sides, contributed to the tragic result."

In a news briefing later at the Pentagon, spokesman George Little said: "For the loss of life and for the lack of proper co-ordination between US and Pakistani forces that contributed to those losses we express our deepest regret.

"We further express sincere condolences to the Pakistani people, to the Pakistani government and, most importantly, to the families of the Pakistani soldiers who were killed or wounded."

At the same briefing, Brig Gen Stephen Clark who led the investigation, said US and Afghan forces had landed in the area to search a village and had been fired upon from a ridge above it.

He said an "overarching lack of trust" between the US and Pakistan had contributed to the breakdown in communication.

Gen Clark said the "first point of failure" was a miscommunication between various command points about whether there were Pakistani troops in the area.

Media playback is unsupported on your device Media caption Islamabad resident: "The US should apologise"

"What they (US headquarters) were told back on the phone is: "We are checking with the BCC (border co-ordination centre) but we are tracking no PakMil (Pakistani military) in the area.

"That was heard at the lower headquarters as: no PakMil are in the area which was then radioed to the ground force commander. (This) began circular reporting back to the regional command who then assumed that the lower echelons had in fact validated and confirmed there was no PakMil in the area."

He said coalition forces had at first staged a "show of force" to make it clear who they were. When firing continued from the ridge, he said, air strikes were carried out.

He said there were three separate engagements before US forces ceased firing.

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He added that the next day troops searched the village and "uncovered a considerable cache" of weapons in connection with the ill-fated operation.

According to a report in the Wall Street Journal, US and Afghan commandos made a series of mistakes on 26 November.

They incorrectly concluded there were no Pakistani forces in the Afghan border area where the coalition was conducting an operation - which cleared the way for a Nato air strike that devastated Pakistani positions.

After the initial strike, the US compounded its mistake by providing inaccurate data to a Pakistani military representative at the border co-ordination centre, missing an opportunity to stop the fighting.

Pakistani officials have denied that their troops on the ridge opened fire first on the commandos.

Furious response

The BBC's Caroline Wyatt in Kabul says it appears that Nato officials did not inform Pakistan of the operation in advance, after fears that the Pakistani military were leaking information to insurgents.

Pakistan responded furiously to the killings of its soldiers.

As well as shutting its border with Afghanistan, which Nato relies on heavily for deliveries of fuel, ammunition and other supplies, it also refused to attend the Bonn conference on Afghanistan earlier this month.

The US government has so far refused to apologise to Pakistan for the deaths, although Washington has repeatedly expressed its condolences for the loss of life.

"Our focus now is to learn from these mistakes," the Department of Defense statement said.

"More critically, we must work to improve the level of trust between our two countries. We earnestly hope the Pakistani military will join us in bridging that gap."