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. BBC correspondents say the admission is expected to embarrass the US military.
In retaliation for the killings, Pakistan has closed its border with Afghanistan, cutting Nato supply lines.
There was no immediate response from Pakistan to the findings of the US investigation. Pakistan, 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.
"This, coupled with other gaps in information about the activities and placement of units from both sides, contributed to the tragic result."
According to a report in the Wall Street Journal with more details, 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 a border co-ordination centre, missing an opportunity to stop the fighting.
The report says the 150-man US and Afghan commando team came under attack from positions along a ridge. The team requested a show of force from the air, wrongly understanding from a radio transmission from Nato that there were no Pakistani military in the area. More
