Pakistan on Sunday buried 24 troops killed in a NATO cross-border air raid that has pushed a crisis in already-strained relations with the United States toward rupture.

The attack was the latest perceived provocation by the United States, beginning with the secret raid that killed al-Qaida leader Osama bin Laden in May, and the question is whether ties will break or whether the two sides will remain stuck in a bad marriage of convenience.

NATO helicopters and fighter jets attacked two Pakistan military outposts on Saturday, killing the soldiers in what Pakistan said was an unprovoked assault.

NATO and U.S. officials expressed regret about the deaths of the Pakistani soldiers, but the exact circumstances of the attack were unclear.

U.S. stabs Pakistan in the back, again, said a headline in the Daily Times, reflecting fury over the attack in Pakistan, a regional power seen as critical to U.S. efforts to stabilize neighboring Afghanistan.

Television stations showed the coffins of the soldiers draped in green-and-white Pakistani flags in a prayer ceremony at the headquarters of the regional command in Peshawar.

Pakistan shut down NATO supply routes into Afghanistan -- used for sending in nearly one-half of the alliance's land shipments -- in retaliation for the worst such attack since Islamabad uneasily allied itself with Washington following the Sept. 11, 2001, terrorist attacks on the United States.

That is unlikely to cool tempers in a country where anti-American sentiment runs high even when ties between Islamabad and Washington are smooth.

About 500 members of Jamaat-e-Islami, Pakistan's most influential religious party, staged a protest in the Mohmand tribal area, where the NATO attack took place.

Down with America and Jihad is the only nnswer to America, they yelled.

Around 40 troops were stationed at the outposts at the time of the attack, military sources said. Two officers were reported among the dead.

They without any reasons attacked on our post and killed soldiers asleep, said a senior Pakistani officer, requesting anonymity.

Blunt Statements

The border is often poorly marked, and Afghan and Pakistani maps have differences of several kilometers in some places, military officials have said.

Pakistan responded with unusually blunt statements condemning the incident as a violation of its sovereignty, and it reserved the right to retaliate.

Pakistan is a vital land route for nearly one-half of NATO supplies shipped overland to its troops in Afghanistan, a NATO representative said. Land shipments account for about two-thirds of the alliance's cargo shipments into Afghanistan.

A similar incident on Sept 30, 2010, killed two Pakistani service personnel, leading to the closure of one of NATO's supply routes through Pakistan for 10 days. NATO apologized for that incident, which it said happened when NATO gunships mistook warning shots by Pakistani forces for a militant attack.

U.S. efforts to repair ties with Pakistan have suffered several big setbacks, starting with the unilateral U.S. special-forces raid that killed bin Laden in a Pakistani town where he had apparently been living for years.

Pakistan condemned the secret operation as a flagrant violation of its sovereignty, while suspicions arose in Washington that members of Pakistan's military intelligence had harbored the al-Qaida leader.

The military came under unprecedented criticism from both Pakistanis, who said it failed to protect the country, and American officials, who said bin Laden's presence was proof the country was an unreliable ally in the war on militancy.

Pakistan's army, one of the world's largest, may see the NATO incursion from Afghanistan as a chance to reassert itself, especially since the deaths of the soldiers are likely to unite generals and politicians, whose ties are normally uneasy.

Pakistan's jailing of a CIA contractor, Raymond Davis, and U.S. accusations that Pakistan backed a militant attack on the U.S. embassy in Kabul have added to the tensions.

From Raymond Davis and his gunslinging in the streets of Lahore to the Osama bin Laden incident, and now to the firing on Pakistani soldiers on the volatile Pakistan-Afghan border, things hardly seem able to get any worse, said the Daily Times.

On the one hand, Islamabad depends on billions in U.S. aid; on the other hand, Washington believes Pakistan can help it bring about a peace in Afghanistan ahead of a combat troop withdrawal at the end of 2014.

The fact is that such incursions of our sovereignty have become routine and we have become so dependent on the U.S. that we just have to grin and bear it, said an editorial in Pakistan's Express Tribune.

(Additional reporting by Zeeshan Haider in Islamabad and Ijaz Mohmand in Peshawar; Writing by Michael Georgy; Editing by Chris Allbritton)