Updated

Pakistani officials at a border coordination center gave the go-ahead to American airstrikes that killed 24 Pakistan troops, unaware that their own forces were in the area, according to U.S. officials briefed on the preliminary investigation.

U.S. officials, giving their first detailed explanation of the worst friendly-fire incident of the 10-year-old war in Afghanistan, said Thursday that an Afghan-led assault force that included American commandos was hunting Taliban militants when it came under fire from an encampment along the Afghan-Pakistan border.

The commandos thought they were being fired upon by militants. But the assailants turned out to be Pakistani military personnel who had established a temporary campsite, U.S. officials said.

According to the initial U.S. account from the field, the commandos requested airstrikes against the encampment, prompting the team to contact a joint border-control center to determine whether Pakistani forces were in the area, a U.S. official said.

The border-control center is manned by U.S., Afghan and Pakistani representatives who are supposed to share information and head off conflicts. But the U.S. and Afghan forces conducting the Nov. 26 commando operation had not notified the center in advance that they planned to strike Taliban insurgents near that part of the border, the official said.

When called, the Pakistani representatives at the center said there were no Pakistani military forces in the area identified by the commandos, clearing the way for the Americans to conduct the airstrikes, the U.S. officials said.

Officials in Islamabad could not be reached to comment on the U.S. allegations. Pakistan repeatedly has denied its forces fired on the Americans.

To read more on this story, see The Wall St. Journal article here.