Story highlights A Pakistani military spokesman says NATO asked and got permission for the strike

NATO helicopters ended up hitting a different target 6 miles away where troops were

He calls it inexplicable copters returned after Pakistan told NATO it was under attack

U.S. forces struck after being told no troops were there, U.S. officials say

U.S. and Pakistani officials both said Friday there was communication between the two sides before a controversial, fatal airstrike last weekend, but they differed on the content of those conversations, with a Pakistani military spokesman saying the attack hit the wrong target.

Some 24 Pakistani troops were killed in the November 26 strike, which has prompted vigorous criticism in Pakistan and spurred its prime minister, Yousuf Raza Gilani, to say that Islamabad is now reevaluating its relationship with Washington.

According to two U.S. officials familiar with an initial assessment of the incident, U.S. commandos were working alongside Afghan troops when they came under fire. The troops did not tell Pakistani authorities about the mission ahead of time, because they thought it would take place entirely within Afghanistan.

The U.S. officials declined to be identified, citing the sensitive nature of the information. They also stressed that a more thorough investigation is ongoing, which could turn up new information. That probe, headed by U.S. Air Force Brig. Gen. Stephen Clark, is due on December 23.

Before calling in airstrikes, the U.S. forces checked with a Pakistani liaison team. They were not seeking permission -- because the airstrikes were described as a matter of self-defense -- but were making sure that Pakistani troops weren't in what was called a poorly marked border area, the officials said.

After that consultation, the U.S. believed there were no Pakistani forces nearby and initiated the airborne attack.

NATO later called the subsequent mass casualties caused by the strike "tragic (and) unintended." U.S. Secretary of State Hillary Clinton and Defense Secretary Leon Panetta have called the incident a "tragedy" and offered condolences, though Washington has not issued a formal apology.

One of the U.S. officials said it wasn't clear if the Pakistanis just didn't know their forces were in the vicinity or didn't understand the location the U.S. forces were talking about.

"Mistakes were made on both sides," one U.S. official said.

Maj. Gen. Athar Abbas, a Pakistani military spokesman, insisted Friday that NATO, not Pakistan, made the fatal mistake. He confirmed, in an interview on Pakistan's Dunya news channel, that there were back-and-forth talks.

U.S. officials who were asked for clearance to strike in a location known as Gola Paraya were told by Pakistan, "We don't have our troops there, you can start your operation if you want," according to Abbas.

Instead, the strike took place 10 kilometers (about six miles) south of Gola Paraya, in Silala. Abbas said a NATO officer later apologized for the alleged error.

After the helicopters came in, Pakistani forces told NATO that one of its checkpoints was under attack, the military spokesman said. The copters turned back after the firing stopped, only to return to target a second military outpost, Abbas said.

"Returning back (with) helicopters and attacking the second check-post was beyond our understanding." he said.

A U.S. official on Friday suggested that the strike's targets were not standard military outposts, but more like "encampments." "There were a bunch of tents, there was no base, there was no walled compound," the official said.

Pakistani officials, for their part, have consistently criticized the strike. In recent days, in fact, they have taken more and more steps aimed at the military coalition -- which continues to be active in Afghanistan and also has gone at times into Pakistan, including for the mission that killed al Qaeda leader Osama bin Laden this year.

That continued Friday, when Pakistani Foreign Minister Hina Rabbani Khar said that NATO and International Security Assistance Force supplies would no longer be routed through Pakistan.

Pakistan's Cabinet and its defense committee unanimously approved this measure, which mirrors a parliamentary resolution passed in May after U.S. forces killed bin Laden in Abbottabad without Pakistan's consent. Parliament would have to approve a reversal of this new policy, Khar said.

"We want to be partners with the world, in this effort to bring peace and stability to the region. But not at the cost of Pakistan's own sovereignty and territorial integrity," she told reporters.

The implementation of this policy follows like-minded, if less definitive, moves made this week.

Specifically, Pakistani authorities turned back 300 trucks carrying NATO supplies and fuel into Afghanistan on Monday. The next day, the Cabinet "noted with satisfaction" that supply lines had been closed and a request had been made for the United States to vacate the Shamsi Air Base.

Pakistan has also decided to boycott a conference on the future of Afghanistan set for next Monday in Bonn, Germany -- a determination made days ago and affirmed Friday by the Pakistani parliament's National Security Committee.

Khar spoke by phone Friday evening with German Foreign Minister Guido Westerwelle about this decision, according to a news release from the Pakistani Foreign Ministry. During that conversation, the Pakistani foreign minister "conveyed her appreciation for German commitment to peace and stability in Afghanistan," the brief statement said.