ISLAMABAD - The U.S. and Pakistan are almost certain a U.S. missile strike killed the head of Pakistan's Taliban and that his death led to a fierce power struggle among his deputies, officials said Sunday, despite claims and counterclaims as to the fate of the country's most wanted man.

Government and intelligence officials, as well as some Taliban commanders and at least one rival militant, have said Baitullah Mehsud likely died in Wednesday's drone strike on his father-in-law's house in northwestern Pakistan's rugged, lawless tribal area near the Afghan border.

President Barack Obama's national security adviser, James Jones, said the U.S. was 90 per cent confident Mehsud had been killed. But three Taliban commanders - Hakimullah, Qari Hussain, who is known for training suicide bombers, and Taliban spokesman Maulvi Umar - called AP reporters Saturday insisting Mehsud was alive.

Neither side has produced any concrete evidence, and the claims were impossible to verify.

There also were conflicting reports that a major fight had broken out between rival Taliban factions during a meeting, or shura, to select Mehsud's replacement, and that one or two of the most likely contenders - Hakimullah and Waliur Rehman - had either been killed or wounded.

The meeting was in the Waziristan region in Pakistan's tribal region, a mountainous area off-limits to journalists where the reach of the government is tenuous or nonexistent.

While it was unclear whether there had been a dispute at all - one Taliban commander, Noor Sayed, denied there had been any disagreement - any succession battle for the top slot in Pakistan's Taliban is likely to be fierce and potentially bloody.

Mehsud's Tehrik-e-Taliban Pakistan is not a single, cohesive group. Rather, it is a loose alliance of tribal groups that often have disputes and power struggles between each other, so removing the man who co-ordinated the factions could lead to intense rivalry over who would succeed him. It could be in the interests of top commanders to deny their leader was dead until they could agree on who would replace him.

Rahumullah Yousafzai, a prominent journalist and expert on the Taliban, said Mehsud's apparent death, and possible divisions among commanders, were a good sign for the government.

"It is now also an opportunity for the Pakistani intelligence that they can create even more splits in Taliban ranks," he said.

"There is no strong leader like (Mehsud) who can hold the Tehrik-e-Taliban in Pakistan together," he added.

Two intelligence officials and two Taliban sources told an AP reporter that a series of shuras were held in various locations in South Waziristan. They said that while the meetings had been attended mainly by local commanders in the initial days, Sunday's shura was also attended by Afghan Taliban representatives and Arab fighters to resolve differences over Mahsud's succession.

The officials spoke on condition of anonymity because of the sensitivity of the situation. None of their claims could be independently verified.

The U.S. drone strike also sparked an anti-American protest Sunday in the northwestern frontier town of Peshawar, with about 8,000 supporters of the hard-line Islamist party Jamaat-e-Islami taking to the streets to denounce what they called U.S. interference in Pakistan's affairs and demand an end to drone strikes.

Pakistan publicly opposes the missile strikes, saying they anger local tribes and make it harder for the army to operate. Still, many analysts suspect the two countries have a secret deal allowing the strikes.

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Associated Press writers Ishtiaq Mahsud in Dera Ismail Khan, Zarar Khan and Ashraf Khan in Islamabad, and Riaz Khan in Peshawar contributed to this report.