Relatives of Pakistani soldier Havildar Mumtaz Hussain. who was killed in a NATO air strike, gather in front of his grave in the village of Bhagwal, south-east of Islamabad.
A NATO investigation into an air strike that killed 24 Pakistani soldiers last month concluded that both alliance and Pakistani forces made mistakes in the incident, NATO said Thursday.
NATO's military chain of command voiced its "sincerest, heartfelt condolences to the families" of the victims, the alliance said in a statement following the November 25-26 incident which has severely strained US-Pakistani relations.
"The investigation has ascertained 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," NATO said.
In a separate statement, the US Defense Department said a lack of proper coordination contributed to the incident and that the two sides must address "the fundamental trust still lacking between us".
The incident heightened tensions in an already fragile relationship, with Islamabad cutting off critical NATO supply routes to Afghanistan and Pakistani officials alleging deliberate US targeting of their troops at border posts.
Placing blame on both US and Pakistani forces could further enrage Islamabad, where officials have maintained their troops did nothing wrong, and did not fire first.
NATO said Afghan and foreign forces "legitimately responded in self-defense" after being initially fired upon by "unidentified forces" that were not believed to be Pakistani military at the time.
"The combined force did not knowingly fire at the Pakistani forces," it said in a statement issued by its SHAPE military headquarters in Mons, Belgium.
While taking fire, NATO forces radioed a Pakistani military liaison to find out if they were being shot at by Pakistani soldiers, SHAPE spokesman Colonel Gregory Julian told AFP.
But the NATO troops gave the wrong coordinates to the Pakistani liaison, Julian said.
"Because of the error he responded correctly that no troops were there," he added.
The investigation found that the Pakistani military, in turn, had failed to tell NATO in advance about the existence of the border post, he added.
The NATO statement said the probe "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."
Pakistan rejected an invitation to cooperate in the US-NATO investigation.
NATO said a thorough review of the operational plan and communications during the incident "substantiate the conclusion that the Pakistani forces were not knowingly targeted and the action of our forces was legitimate within the laws of armed conflict and within their rules of engagement."
The NATO mission has taken "immediate steps" to avoid similar incidents in the future and is continuously working to improve liaison with Pakistani forces.
The International Security Assistance Force (ISAF) in Afghanistan is reviewing the "manning, training, and certification" of Border Coordination Centres that enable NATO and Pakistani troops to communicate.