The officials told The Wall Street Journal they received incorrect information from the U.S. military on the target. The newspaper reported earlier U.S. officials said Pakistan authorized the strike, apparently unaware Pakistani soldiers were in the Mohmand tribal area near the border with Afghanistan.
The incident, being investigated by NATO, has drawn much Pakistani outrage and further aggravated already strained U.S.-Pakistani relations.
Pakistan said NATO military officials in the area apologized for the strike in private, the Journal said. They also said the border posts hit by the strike were permanent ones and not temporary camps.
The Journal, citing U.S. sources who had received a preliminary briefing, said an assault force led by Afghan security forces, which included U.S. commandos, had been hunting Taliban militants when they came under fire from an encampment along the border. The assault force thought the fire was coming from the militants, but U.S. officials told the Journal the assailants turned out to be Pakistani military personnel who had established a temporary campsite.
Initial U.S. accounts from the field said the commandos, seeking an airstrike, contacted a joint border-control center to find out whether Pakistani forces were in the area, a U.S. official told the Journal. The official said the assault force had not given advance notice to the center about its operation against Taliban insurgents.
When contacted, the Pakistani officials at the center advised there were no Pakistani military forces in the area, thus allowing the airstrike to proceed, the U.S. officials said.
Pakistan has repeatedly denied its forces fired on the Americans and claimed the airstrike was unprovoked.
U.S. officials acknowledged there were errors by both sides in the incident, adding the Pakistani deaths were a terrible accident.
"There were lots of mistakes made," the official said. "There was not good situational awareness to who was where and who was doing what."
U.S. officials speaking to the Journal said the account about the airstrike was based largely on interviews with the commando team and could change when more information is received.
A formal report on the airstrike by U.S. military investigators is due by Dec. 23.
Pakistan, protesting the airstrike, has decided against attending next week's international conference on Afghanistan in Bonn, Germany. The government had closed its supply routes for the coalition forces in Afghanistan.