However, at the same time, the investigation conducted by a senior officer of the US Central Command noted that inadequate co-ordination between US and Pakistani military resulted in misunderstanding about the true location of the Pakistan military units.
Department of Defense in a statement issued in the wee hours expressed its regret.
The results of the investigation have been shared with Pakistan, which did not participate in it expressing its doubts at transparency and credibility.
"The investigating officer found that US forces, given what information they had available to them at the time, acted in self-defense and with appropriate force after being fired upon," the US Department of Defense said.
"He also found that there was no intentional effort to target persons or places known to be part of the Pakistani military, or to deliberately provide inaccurate location information to Pakistani officials," the statement said.
"Nevertheless, inadequate coordination by US 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," it said.
This, coupled with other gaps in information about the activities and placement of units from both sides, contributed to the "tragic" result, the Pentagon said.
"For the loss of life -- and for the lack of proper coordination 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," the Department of Defense statement said.
Noting that its focus now is to learn from these mistakes and take whatever corrective measures are required to ensure an incident like this is not repeated, the Pentagon said the chain of command will consider any issues of accountability.
"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 Pentagon said.
The NATO attack had triggered an angry reaction in Pakistan and the government closed all NATO supply routes and forced the US to vacate Shamsi airbase in Balochistan province, which was reportedly used by CIA-operated drones.
Pakistan has now sought "new terms of engagement" with US that guarantees the country's sovereignty and ensures that there is no unilateral action like the raid that killed Osama bin Laden.