(REUTERS) - Pakistan, enraged by a NATO cross-border attack that killed 24 soldiers, could end support for the U.S.-led war on militancy if its sovereignty is violated again, the foreign minister said, warning enough is enough.

The South Asian nation has already shown its anger over the weekend strike by pulling out of an international conference in Germany next week on Afghanistan, depriving the talks of a central player in efforts to bring peace to its neighbor.

Enough is enough. The government will not tolerate any incident of spilling even a single drop of any civilian or soldier's blood, The News newspaper on Thursday quoted Foreign Minister Hina Rabbani Khar as telling a Senate committee on foreign affairs.

Pakistan's role in the war on terror must not be overlooked, Khar said, suggesting Pakistan could end its support for the U.S. war on militancy. Despite opposition at home, Islamabad backed Washington after the Sept. 11 attacks on the U.S.

The U.S. Embassy released a video statement on YouTube by Ambassador Cameron Munter in which he expressed regret for the attack.

I would like to extend my most sincere condolences to the people and government of Pakistan, and especially to Pakistan's men and women in uniform, for the tragic incident that took place on Nov. 26 in Mohmand Agency, he said, standing in front of U.S. and Pakistani flags.

We regret it very much, he added in Urdu.

He said the U.S. took the attack very seriously and pledged a full, in-depth investigation.

Pakistan and the U.S. have stood together for over 60 years, he said. We have weathered previous crises together. I'm certain we will weather this one too, and emerge, together, as stronger partners.

But events seemed to be working against lowering tensions. Two Pakistani men were killed in Afghanistan early on Thursday and Pakistani border guards said NATO may have been responsible.

The officials said the two men, who were from the town of Chagai in the Pakistani province of Baluchistan, were gathering wood 30 km (18.6 miles) inside Afghanistan. They said NATO helicopters fired on their vehicle.

I can confirm that the bodies of two residents of Chagai have arrived from Afghanistan, said Chagai Assistant Commissioner Tufail Baloch. But I do not have any information on how they were killed. It happened on Afghan soil so we don't have many details yet.

NATO officials had no immediate comment.

NATO helicopters and fighter jets attacked two military border posts in northwest Pakistan on Saturday in the worst incident of its kind since 2001.

The top U.S. military officer denied allegations by a senior Pakistani army official that the NATO attack was a deliberate act of aggression.

General Martin Dempsey, chairman of the U.S. military's Joint Chiefs of Staff, told Reuters in an interview: The one thing I will say publicly and categorically is that this was not a deliberate attack.

The incident has given the army, which has ruled Pakistan for more than half of its history and sets security and foreign policy, some breathing room after facing strong criticism from both the Pakistani public and the U.S. after bin Laden was killed in a secret raid by U.S. special forces in May.

The al Qaeda leader had apparently been living in a Pakistani garrison town for years.

Pakistanis criticized the military for failing to protect their sovereignty and U.S. officials wondered whether some members of military intelligence had sheltered him. Pakistan's government and military said they had no idea bin Laden was in the country.

Protests have taken place in several cities every day since the NATO strike along the poorly-defined border, where militants often plan and stage attacks.

Pakistan military sources said Islamabad had canceled a visit by a 15-member delegation, led by the Director General of the Joint Staff, Lieutenant-General Mohammad Asif, to the U.S. that was to have taken place this week.

In an apparently unrelated attack, a bomb blew out a wall of a government official's office in Peshawar, the last big city on the route to Afghanistan, early on Thursday, police said. There were no reports of casualties.

Also in the eastern Afghan province of Logar, unknown gunmen abducted seven Pakistani engineers in Pul-e Alam, said provincial police chief Gulam Sakhi Rogh Lewanai.

The U.S. has long wanted Pakistan, whose military and economy depend heavily on billions of dollars in American aid, to crack down on militant groups that cross its unruly border to attack Western forces in Afghanistan.

More recently, U.S. Secretary of State Hillary Clinton asked Pakistan to bring all militant groups to the negotiating table in order to stabilize Afghanistan.

The NATO attack makes Pakistani cooperation less likely.

NATO hopes an investigation it promised will defuse the crisis and that confidence-building measures can repair ties.

Critics say Pakistan has created a deadly regional mess by supporting militants like the al Qaeda-linked Haqqani network to act as proxies in Afghanistan and other groups to fight Indian forces in the disputed Kashmir region.

Pakistan says it has paid the highest price in the war on militancy. Thousands of soldiers and police have been killed.

The sacrifices rendered by Pakistan in the war on terror are more than any other country, Khar was quoted as saying. But that does not mean we will compromise on our sovereignty.

(Additional reporting by Jibran Ahmad in PESHAWAR, Obaid Omar in PUL-E ALAM and Emma Graham-Harrison in KABUL; Writing by Michael Georgy and Chris Allbritton; Editing by Nick Macfie)

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