U.S. defense officials Thursday blamed inadequate coordination by both Pakistani and U.S.-led forces for last month's coalition attack that killed 24 Pakistani soldiers at Pakistan's border with Afghanistan.

Pentagon spokesman George Little said the investigation found that U.S. forces, given the information they had available to them at the time, acted “in self-defense and with appropriate force after being fired upon.”

He said U.S. officers had shared incorrect mapping information with the Pakistanis, leading to a misunderstanding about the location of Pakistani military posts along the border. That, he said, along with other gaps in information about the activities and location of units from both sides, contributed to “the tragic result.”

But the investigation found that there was “no intentional effort” by U.S. forces to mislead or target the Pakistani military.

The U.S. Department of Defense expressed its “deepest regret” and “sincere condolences” for the incident, but stopped short of meeting the Pakistani demand for a full apology.

The attack on November 26 has inflamed already damaged tensions between the U.S. and Pakistan. Islamabad has ordered U.S. forces to vacate a Pakistani airbase they were using, and has indefinitely closed the two main overland routes NATO uses to send nonlethal supplies to Afghanistan.

American media reports on Thursday quoted unnamed U.S. officials as saying NATO's failure to inform Islamabad that it was conducting the operation may have led Pakistani soldiers to mistake the coalition forces for Taliban militants.