Miscommunication and bad maps contributed to the deaths of 24 Pakistani troops in a NATO airstrike last month, a military investigation concluded Thursday.
A statement issued by the Pentagon on Thursday said "inadequate coordination by U.S. and Pakistani military officers ... resulted in a misunderstanding about the true location of Pakistani military units."
"This, coupled with other gaps in information about the activities and placement of units from both sides, contributed to the tragic result," Pentagon spokesman George Little said.
The U.S. investigation also conceded a critical error by U.S. troops — telling Pakistan the cross-border shooting was taking place about 9 miles away, due to mapping error. Pakistan responded by saying it had no troops there.
The Pentagon statement expressed "deepest regret" for the loss of life and the lack of coordination that contributed to it. However, it also said U.S. forces cannot operate effectively in Pakistani border areas "without addressing the fundamental trust still lacking between us."
A senior defense official told NBC News on Thursday that the U.S. is taking responsibility for its mistakes and, in keeping with cultural norms in the region, will offer condolence payments to the families of the fallen Pakistani troops.
The death of the Pakistani soldiers dug in along the mountainous, remote border area, along with the initial NATO response, has incensed Pakistanis and marked yet another setback in the Obama administration's efforts to improve chronically troubled ties with an uneasy ally against militants.
The incident prompted Pakistan to shut down ground routes used to supply U.S. forces in Afghanistan and to demand that the United States vacate an air base used to launch drone flights within 15 days.
Pakistani army spokesman Major General Athar Abbas said Thursday that Pakistan does not agree with the U.S findings because they are "short on facts.''
Brigadier General Stephen Clark, who headed the military U.S. investigation, said U.S. aircraft including fighter jets and attack helicopters came under fire late on the night of Nov. 25 as it approached an Afghan village right over the Pakistani border for a routine mission.
After the NATO forces began receiving mortar and machine gun fire from a ridge area, U.S. officials and a Pakistani border liaison officer embedded with NATO forces concluded - acting on an erroneous analysis of where the firefight was taking place - that no Pakistani military involved so they returned fire.
Part of the problem, Clark said, were instructions to U.S. soldiers not to directly share details of their geographic assessments with their Pakistani liaison officers - a symptom of what he called "an overarching lack of trust" on both sides.
When U.S. forces sought a precise location of allied soldiers from a commander in Pakistan, the exchange further illustrated mutual wariness, Clark said.
"When asked, the (Pakistani) general answer back was, 'Well, you know where it is because you're shooting at them,' rather than giving a position."
Video: Angry Pakistanis mourn casualties (on this page)
In a statement released on Thursday, NATO said that a "combined international and Afghan force was initially fired upon by unidentified forces, then believed not to be Pakistani military, and legitimately responded in self-defense."
U.S. officials said General Martin Dempsey, chairman of the U.S. Joint Chiefs of Staff, had a "professional and cordial" conversation with General Ashfaq Kayani, the head of the Pakistani military, about the report on Wednesday night.
Pakistan refused to take part in the investigation, which Clark said had hindered a deeper understanding of the incident.
It is unlikely the conclusions of the report will placate Pakistani military leadership in the charged climate following the incident.
Yet U.S. officials said they would now focus on improving communication with Pakistan and avoiding a repeat of such bloodshed.
"We cannot operate effectively on the border, or in other parts of our relationship, without addressing the fundamental trust still lacking between us," Little said.
"We earnestly hope the Pakistani military will join us in bridging that gap."
Reuters, NBC News and msnbc.com staff contributed to this report.