The U.S.-led coalition in Afghanistan released footage Thursday of a skirmish with militants that Pakistan claims resulted in an airstrike on one of its border posts that killed 11 of its troops.

Pakistan has lodged a strong diplomatic protest, saying the bombing of the Gorparai post in the Mohmand frontier region on Tuesday was a "completely unprovoked and cowardly act."

But Pakistani and U.S. officials have given widely differing accounts of an event that threatens to further sour relations between key allies in Washington's war on terror — a partnership already unpopular among Pakistanis.

To support its version, the coalition on Thursday took the unusual step of releasing excerpts of a video shot by a surveillance drone circling above the mountainous battle zone.

Click here to view the airstrike video.

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The grainy, monochrome images show about a half-dozen men firing small arms and rocket-propelled grenades from a ridge at coalition troops off-camera in the valley below.

According to the voiceover in the video, the ridge is in Afghanistan's Kunar province, about 200 yards from the Pakistan border and close to the Gorparai checkpoint.

Neither the checkpoint nor any other structures are visible in the video excerpts.

The voiceover says the coalition forces were on a reconnaissance mission and returned fire as they tried to break contact and move to a point where a helicopter could pluck them to safety.

The video shows the "anti-Afghan militants" moving to a position identified as inside Pakistan and the impact of a bomb which the voiceover says killed two of them.

The survivors then fled into a ravine, where three more bombs were dropped, nearly three hours after the clash began. The voiceover said all the militants were killed.

One of the bombs fell off screen, and U.S. officials said about a dozen bombs were dropped in all.

On Wednesday, U.S. diplomats offered apologies for the reported casualties. But the Pentagon insisted that the drone footage of the bombings showed they hit their intended targets.

President Bush's national security adviser said Thursday that U.S. officials "have not been able to corroborate" claims by Pakistani officials that a U.S. skirmish with militants along the Afghan-Pakistani border killed 11 Pakistani troops.

"Should it be true, obviously we would be very saddened by that loss," national security adviser Stephen Hadley told reporters traveling with Bush in Europe.

Reflecting how the incident has put the already fragile U.S.-Pakistan relationship on shaky ground, Hadley noted that Pakistan has been an important ally in the war on terror but added that "we hope" that will continue.

Pakistan army spokesman Maj. Gen. Athar Abbas gave a different account.

Abbas said the fighting broke out after Afghan government soldiers who had occupied a mountaintop position in a disputed border zone Monday acceded to a Pakistan request to withdraw.

"They were on their way back and they were attacked by insurgents in their own territory," Abbas said.

He said the Afghans then called in coalition airstrikes, which hit the Pakistani Frontier Corps post across the border.

Many Pakistanis blame their nation's anti-terror alliance with the U.S. for a rise in extremist violence in their country.

In the northwest city of Peshawar, about 50 members of an Islamic student group peacefully protested the U.S. and Pakistani President Pervez Musharraf on Thursday. Bearded men brandished banners with slogans such as "America is the most terrorist country in the world" and "U.S. ally Musharraf, resign immediately."

Dawn, a leading daily newspaper in Pakistan, said in an editorial Thursday that the "incident must be sorted out to end the friction" between Pakistan, the U.S. and NATO officials in Afghanistan, but that "Islamabad must insist that those responsible for this 'cowardly' attack must be made accountable."

Both the main ruling coalition parties have condemned the Mohmand incident.

On Thursday, a spokesman for the second biggest party called the strike "brutal."

"This is against our sovereignty and international norms and we reject it," said Sadiqul Farooq of ex-Prime Minister Nawaz Sharif's party.

U.S.-Pakistan relations should be revised so that there is "no dictation, rather mutual consultation," he said.

Pakistan's newly elected civilian government is negotiating with tribal elders to secure peace with militants along the Afghan border in hopes of curbing a surge in violence. It is a step back from the heavy-handed tactics pursued by the previous government led by supporters of Musharraf.

Western officials fear the peace deals could give more space to Taliban and al-Qaida militants to operate, but Pakistan insists the negotiations are not with terrorists but with militants willing to lay down their arms.