ISLAMABAD: A rare condemnation by the Pakistan army chief of an especially deadly US drone attack and Washington's abrupt dismissal of his concern is a sign of how troubled the strategically vital relationship between the two countries has become.

The public spat, which followed the contentious release of an American CIA contractor who shot and killed two Pakistanis, also highlights the somewhat dysfunctional nature of the relationship. Pakistani officials are often quick to fan the flames of anti-American sentiment, even when they are quietly supporting the United States in the background _ as is believed to be the case with drones.

Growing discord between the two countries could prove ominous for US attempts to get Pakistan to boost its help with the Afghan war. The US wants Pakistan to target on its territory the Taliban militants who regularly attack US troops in Afghanistan or more likely push them to the negotiating table.

''The relationship between Pakistan and the US is becoming very awkward and unsustainable in the way it is proceeding in every aspect,'' said Talat Masood, a former Pakistani army general and political analyst.

Pakistani army chief Gen. Ashfaq Parvez Kayani's strongly condemned Thursday's drone attack close to the Afghan border, saying it killed many innocent civilians.

Pakistan summoned US Ambassador Cameron Munter to protest the attack on Friday, and the government said it would not participate in a trilateral meeting in Brussels with the US and Afghanistan, proposed by Washington for the end of March.

''It is evident that the fundamentals of our relations need to be revisited,'' the Foreign Ministry said in a statement. ''Pakistan should not be taken for granted nor treated as a client state.''

Pakistani intelligence officials initially said the drone attack killed roughly three dozen militants in the North Waziristan tribal area who were discussing plans to send additional fighters across the border in Afghanistan.

But those same officials said Friday that the missiles hit a meeting between two tribes who had gone to the Taliban for help in mediating a dispute over a local chromite mine. A total of 12 Taliban fighters and 24 innocent civilians were killed, said the officials, speaking on condition of anonymity because they were not authorized to talk to the media.

Neither Kayani's statement nor the one issued by the Foreign Ministry mentioned any militant deaths.

A US official familiar with details of the attack denied that innocent people were targeted.

''There's every indication that this was a group of terrorists, not a charity car wash in the Pakistani hinterlands,'' said the official, who spoke on condition of anonymity because the information was classified.

The statement differed sharply from usual US responses to alleged civilian casualties in Afghanistan, where military officials regularly express concern about such reports and promise a thorough investigation.

Some analysts believe Kayani's condemnation may have been intended to deflect criticism of the military's perceived role in releasing the CIA contractor, Raymond Allen Davis, on Wednesday. He was freed after the heirs of his victims received more than $2 million in ''blood money.''

While the army did not play a public role in the deal, it is the most powerful institution in the country and is often seen as pulling the strings in the background. Given Davis' CIA connections, it is hard to believe the army did not sanction or even arrange the deal to free him.

His release sparked anger across Pakistan, especially among right wing and religious parties, which wield significant power.

''I think what happened is Kayani had to protect himself, and I think the US made a mistake carrying out such a large attack only a day after Davis was released,'' said Masood. ''It created a huge embarrassment for the whole power structure in Pakistan.''

Kayani, who has close ties to senior US military figures, rarely issues public statements on US drone attacks, or anything else for that matter.

Pakistani politicians regularly condemn the attacks as violations of the country's sovereignty, but Pakistan's most powerful intelligence agency, which is controlled by the army, is believed to help with some of the strikes, and some of the drones are believed to take off from bases in the country.

Kayani's statement did not mention any role the army may have had in Thursday's attack.