Pakistani officials gave the green light for the Nato strikes that killed 24 of their troops last month, unaware that the forces were in the area, the Wall Street Journal reported on Friday.
The journal cited US officials briefed on the preliminary investigation into the incident — the worst exchange of friendly fire between the two reluctant allies in the decade-long war in Afghanistan.
The officials told the journal that an Afghan-led force including US commandos was pursuing Taliban fighters near the Afghanistan-Pakistan border when they came under fire from what they thought was a militant encampment.
When they called in air strikes on the camp, team members contacted a joint command-and-control center manned by US, Afghan and Pakistani troops, and Pakistani representatives said there were no friendly forces in the area, clearing the way for the air assault, the officials told the Journal.
The officials nevertheless acknowledged errors on both sides.
"There were lots of mistakes made," it quoted an official as saying. "There was not good situational awareness to who was where and who was doing what."
They also cautioned that the latest account is based on initial interviews with the commandos involved and could change as more details come to light.
The Pentagon has insisted there was no deliberate attack on Pakistani forces, but US officials have stopped short of apologizing over the incident.
Pakistan has said the air assault on its soldiers was unprovoked and spread over a period of two hours, despite Pakistani protests to the Americans.
Relations have long been tense between the two allies, with Washington accusing elements of Pakistan's military and intelligence services of collaboration with the Taliban and other Islamist militants.
Pakistan has in turn alleged that US drone strikes aimed at militants have killed scores of civilians, stoking extremism and bolstering its own domestic Islamist insurgency.
The friendly fire incident over the weekend set off the worst crisis in relations between the two countries since US commandos swooped in to kill Al Qaeda chief Osama bin Laden in a Pakistani garrison town in May.