KABUL, Afghanistan — An investigation into a NATO attack that killed 24 Pakistani troops last month near the Afghan border has concluded that a combination of mistrust and bad maps led to the airstrikes on two Pakistani outposts, the U.S. Department of Defense and a NATO official said on Thursday.

It's unclear whether the report, which says mistakes were made on both sides, will reduce the tension between Pakistan and the U.S. over the incident. The Pakistani army has said its troops did nothing wrong and claimed the attack was a deliberate act of aggression.

A statement issued by the U.S. Department of Defense did not apologize for the attack, as the Pakistanis have demanded, and instead defended the actions of American forces.

"The report says we recognize we made mistakes, and that mistakes were also made by the Pakistanis," said the NATO official, who could not be named because the Defense Department's investigation has not yet been made public.

"We have a lot of work to do to improve coordination, and we've already implemented steps to do that," the official said.

The Defense Department said in a statement Thursday that the investigation found U.S. forces — given what information they had available to them at the time — reacted in self-defense and with appropriate force after being fired upon from the direction of the Pakistani border in the Nov. 26 incident.

"Inadequate coordination by U.S. and Pakistani military officers operating through the border coordination center — 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," said the statement, which was released in Washington.

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

NATO, Afghanistan and Pakistan forces use the joint border control centers to share information and coordinate security operations.

Pakistani officials did not immediately respond to requests for comment on the report. Afghan officials also had no immediate comment.

The Pakistani military has said it provided NATO with maps that clearly showed where the border posts were located. It also claimed NATO provided Pakistani liaison officers with the wrong coordinates when the coalition asked if there were any Pakistani troops in the area where the strikes took place.

In Mons, Belgium, NATO's supreme military headquarters, a spokesman said the joint force was fired on by what they thought were insurgents "and legitimately responded in self-defense."

Col. Gregory Julian said the investigation found that their response was legitimate within the laws of war and the troops own rules of engagement. He acknowledged that "a series of mistakes were made on both sides in failing to properly coordinate their locations and actions," both before the operation and during the resulting engagement. He stressed that the joint unit "did not knowingly fire at the Pakistani forces."

"The investigation has substantiated that close air support was employed in self-defense in response to intense, heavy machine gun and mortar fire initiated by what turned out to be Pakistan forces near the border in the vicinity of Salala," an area in Pakistan's Mohmand tribal region.

Since the Nov. 26 attack, a furious Pakistani government has shut down NATO supply routes to Afghanistan and thrown the U.S. out of its Shamsi Air base in southwestern Baluchistan province. The base was used to maintain drones used in strikes against insurgents hiding in safe havens in Pakistan's lawless tribal belt on the Afghan frontier.

The Pakistani border closure forced the U.S. and NATO to reorient their entire logistics chains to the so-called Northern Distribution Network through Russia and Central Asia.

For most of the 10-year war in Afghanistan, 90 percent of supplies shipped to the international force came through Pakistan, via the port of Karachi. But over the past three years, road and rail shipments from NATO's European members via Russia and the Central Asian nations have expanded, and before the border incident accounted for more than half of all overland deliveries.

"For the loss of life — and for the lack of proper coordination between U.S. 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," the U.S. statement said.

It added that the military's focus would now be to learn from the mistakes and "take whatever corrective measures are required to ensure an incident like this is not repeated."

"More critically, we must work to improve the level of trust between our two countries. We cannot operate effectively on the border — or in other parts of our relationship — without addressing the fundamental trust still lacking between us. We earnestly hope the Pakistani military will join us in bridging that gap," the statement said.

The NATO official said the incident occurred after a company-sized joint U.S.-Afghan commando unit operating in the Afghan side of the border in eastern Kunar province came under fire from the direction of the border. A company is about 150 troops.

The unit, which could not withdraw safely due to the nature of the terrain, then attempted to determine that the fire wasn't coming from anywhere near Pakistani positions, in order to avoid hitting them, the official said.

At that point "mistakes were made" because different mapping systems were used to determine the exact location of the firefight, he said. Discrepancies on how the border was marked on different maps led the unit to believe they could safely return fire. They then called in airstrikes from F-15 fighter bombers, Apache attack helicopters and an AC-130 Spectre gunship.

"There was also an element of mistrust that contributed to the mistakes," the official said, citing the report.

Associated Press writer Sebastian Abbot contributed to this report from Islamabad. Slobodan Lekic can be reached on Twitter at http://twitter.com/slekich