Pakistan, a staunch ally in the U.S.-led war on terrorism, denounced Tuesday's attack on a border post in the Mohmand tribal region as "unprovoked and cowardly" and said it had undermined the cooperation in the battle against al Qaeda and the Taliban.

Elders from ethnic Pashtun tribes in Mohmand, one of seven semi-autonomous tribal regions, issued a statement late on Thursday condemning the attack as "naked aggression" and said they were ready to raise a "lashkar", or tribal army.

"It's the duty of the government to protect and defend the frontiers and we are ready to raise a lashkar to help our army in their cause," the elders said.

"We are ready to fight for our homeland as we fought in Kashmir in 1948," it said, referring to the first war between Pakistan and India just a year after their independence from British rule.

The soldiers killed were manning a border post around 35 km (22 miles) northwest of Ghalanai, Mohmand's main town.

U.S.-led ground forces from across the border in the eastern Afghan province of Kunar called for air support after coming under small-arms and rocket-propelled-grenade (RPG) fire from militants occupying a ridge 200 metres (yards) inside Pakistani territory.

GRAINY IMAGES

A video released by the NATO-led forces showed footage of the encounter shot by a reconnaissance drone aircraft, complete with a voice-over describing the incident.

The video was posted on the internet site here

The somewhat blurred, grainy images showed between five and seven figures scurrying among the rocks along the ridge, and flashes of gunfire and from RPGs, according to the American military commentary.

In the final sequences, four precision bombs were shown exploding, but the commentator asserted that no military structure or posts were in the impact areas.

The U.S. military said the operation was coordinated with Pakistan and the Pentagon defended U.S. forces, saying initial indications pointed to a "legitimate strike" carried out in self-defence after they came under attack.

Pakistan denied the U.S. version that the offensive was coordinated and summoned U.S. Ambassador Anne Patterson to the foreign ministry to a lodge protest on Thursday.

U.S. Defense Secretary Robert Gates said on Thursday he regretted that a U.S. air strike killed 11 Pakistani soldiers, and invited Pakistani and Afghan officials to help investigate the incident.

"Pakistan is an incredibly important partner for us in this war on terror and personally I regret that we've had something that has created a problem," Gates told reporters on the sidelines of a NATO defence ministers meeting in Brussels.

Pilotless drones have carried out several strikes targetting al Qaeda militants inside Pakistan's tribal areas.

The casualties suffered by Pakistani security forces in Tuesday's attack was by far the worst in the nearly eight years since the alliance was formed in 2001.

Authorities in the North West Frontier Province, bordering Afghanistan, have called for a review of cooperation with Washington if such attacks continued.

A new Pakistani government, led by the party of assassinated former prime minister Benazir Bhutto, has been negotiating with ethnic Pashtun tribes to get them to press the militants to give up a campaign of violence in Pakistan in which hundreds of people have been killed over the past year.

Pakistan's Western allies, notably the United States, have voiced concerns over the pacts, saying such agreements enable militants to regroup and step up cross-border attacks from Pakistani soil.