Pakistan accused US forces yesterday of killing 11 of its soldiers in an “unprovoked and cowardly” attack on a border post, an act that it said threatened to undermine the two countries’ joint effort in the War on Terror.

The soldiers were killed late on Tuesday night in what American officials called a “regrettable incident” at Gora Pai in the Mohmand tribal region of Pakistan, bordering the Afghanistan Kunar province, where coalition forces have been fighting Taleban insurgents.

A senior Pakistani security official said the fighting erupted after Afghan and Nato forces tried to set up a mountain-top post along a disputed stretch of the frontier and were told by border troops to withdraw.

A group of militants attacked the coalition troops as they were retreating and American assault helicopters came to their aid, killing eight insurgents. However, some of the missiles hit the Pakistani checkpoint and destroyed it.

This was the most Pakistani soldiers killed in an attack by US-led coalition forces, and Islamabad used its strongest language yet to condemn the American actions as violating its sovereignty.

“We will take a stand for sovereignty, integrity and self-respect and we will not allow our soil [to be attacked],” Yousaf Raza Gilani, the Prime Minister, told Parliament.

“The violent attack hit at the very basis of co-operation and sacrifice with which Pakistani soldiers are supporting the coalition forces,” Major-General Athar Abbas, the chief military spokesman, said.

He denied that the insurgents had struck from Pakistan or that there had been any attack launched from the border post. He also denied that the coalition had given prior notice of its operation in the area. Major General Abbas said Afghan army forces had come under attack inside Afghanistan as they were withdrawing at Pakistan’s request after setting up a military post in the disputed border region. “They were on their way back and they were attacked by insurgents in their own territory,” he said.

The US military confirmed that it had used artillery and air-strikes in self-defence after its forces had come under fire from the Taleban. “Shortly after the attack began, coalition forces informed the Pakistan Army that they were being engaged by anti-Afghan forces in a wooded area near the Gora Pai checkpoint,” the Pentagon said in a statement.

“At that same time, an unmanned aerial system also identified anti-Afghan forces firing at coalition forces. In self-defence, coalition forces fired artillery rounds at the militants.”

Washington later softened its tone, describing the air-strike as a regrettable incident. “We’re sad to see the loss of life among the Pakistani military, who are our partners in fighting terror,” Gonzalo Gallegos, a State Department spokesman, said.

Unlike other tribal regions, Mohmand has not been a hotbed of al-Qaeda, though there has been marked rise in the militant influence in the area.

The latest incident came amid growing tensions between American and Pakistani forces. Pakistan has been a key US ally in the War on Terror, but cross-border attacks have put a serious strain on the alliance.

Afghan and Nato forces accuse Islamabad of failing to stop infiltration by Taleban fighters who take refuge in the tribal belt along the frontier, and they are concerned that the Pakistani Government’s recent peace talks with militants will only give the insurgents more room for manoeuvre.

American military officials said that there had been a threefold increase in attacks by insurgents in the recent months. They maintain that peace pacts enabled militants to regroup and set up attacks into Afghanistan from their sanctuaries across the border.

Pakistan, for its part, has been angered by an upsurge of activity by US drones within its borders, though the US says that such missions have recently scored some significant successes. Using Predator unmanned aerial vehicles (drones), armed with Hellfire missiles, the Americans have had two confirmed “kills” in the past few months.

The first was Abu Laith al-Libi, head of the Libyan fighting group of al-Qaeda, who was killed by a missile fired from a Predator while he was in Pakistan. The Libyan had a reputation for being a charismatic and respected religious figure and an experienced operational planner.

Abu Suleiman al-Jaziri, another al-Qaeda commander to be killed by a Predator in the tribal areas this year, was an Algerian known to have trained British Muslims who travelled to Pakistan for terrorist instruction.

However, the use of Predators to launch air attacks in Pakistan remains a highly controversial strategy because they have killed many civilians and are alienating the population further against the Americans.

Pakistan has lost about 1,000 soldiers fighting militants in border mountains that have never come under the control of any government. Islamabad maintains that US air-strikes targeting suspected militants in the tribal areas only inflame the situation.

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