The killing of one of Pakistan's most wanted militant in a US drone strike has exposed centuries-old rivalries within the group he led, the Pakistani Taliban, making the insurgency ever more unpredictable and probably more violent.

Hakeemullah Mehsud's death this month has set off a power struggle within the outfit's ranks, which could further unnerve a region already on tenterhooks with most US-led troops pulling out of neighbouring Afghanistan in 2014.

When a tribal council declared Mullah Fazlullah as the new leader of the Pakistani Taliban last week, several furious commanders from a rival clan stood up and left.

"When Fazlullah's name was announced, they ... walked out saying, 'The Taliban's command is doomed'," said one commander who attended the Nov 7 'shura' meeting in South Waziristan.

Others at the shura declared loyalty to the hardline new leader and stayed on to map out a plan to avenge Hakeemullah's death through a new campaign of bombings and shootings.

"This is the start of our fight with the Pakistan government, an American puppet," the Taliban official said.

"Those who forced the Soviet Union out of Afghanistan are capable of breaking up Pakistan," he added, alluding to senior commanders whose rite of passage into war started with the rebellion against Soviet troops in Afghanistan in the 1980s.

The Pakistani Taliban have always been divided, a loose alliance of militant bands united only by extremist beliefs and their hatred of the government. The group operates independently of its Taliban allies in Afghanistan, who are fighting US-backed forces there.

But the death of Hakeemullah, a member of the dominant Mehsud tribe, and the rise of Fazlullah, a Swat Valley native and hence an outsider in the eyes of tribesmen, changes the picture in the Tehrik-i-Taliban Pakistan (TTP), or Pakistani Taliban.

Under Hakeemullah, the TTP had been open to the idea of peace talks with the Pakistani government, even though no meaningful negotiations had taken place.

Fazlullah ruled out any talks and declared the start of a new campaign to attack government and security installations in Punjab, Prime Minister Nawaz Sharif's political base.

"Mehsuds are not only not happy with this appointment but there are reports of serious infighting among them that might come to the fore in the near future," said Saifullah Mehsud, director of the Pakistani think tank Fata Research Center.

"I think for now the anti-peace talks group among the TTP has prevailed and hence the appointment of Fazlullah," said Saifullah, who compiles data based on information provided by his sources on the ground in the tribal Pashtun areas.

Afghan links

Fazlullah's threat against Punjab has unnerved Pakistan's most prosperous and populous province, where attacks have so far been rare.

Various Pakistani militant groups, including the Sipah-i-Sahaba, Lashkar-i-Jhangvi and Jaish-i-Mohammad, are based around Punjab and appear to have been long tolerated by Pakistan's powerful military and intelligence establishment.

Some of them are said to have been formed to fight Indian forces in disputed Kashmir, but they have turned on Pakistan in recent years thanks to the growing influence of the TTP and Al Qaeda, and have become increasingly involved in Taliban affairs.

"The situation is getting out of control and the ISI knows that," said one Western diplomat in Islamabad, referring to the Pakistani military's powerful intelligence arm.

As the dynamic within the militancy evolves, powerful Punjabi groups are also beginning to turn their heads westwards, with many seeing the pullout of US troops from Afghanistan as a chance to expand their reach to tribal areas.

During a recent meeting with Reuters in the city of Mardan, a group of militants -- who sat cross-legged on the floor of a mud-brick safe house sipping tea and eating biscuits -- said the Afghan cause was close to their hearts

"We want peace in Afghanistan under Mullah Omar's leadership," said Abdurakhman, a militant with Jaish-i-Mohammad, a group usually focused on Kashmir, others nodding in agreement. Mullah Omar is the chief of the Afghan Taliban.

"When the Americans leave, elders will sit down with Mullah Omar and decide. If there is a need to fight, we will recruit and send people there."

Sitting next to him, Farhatullah, a middle-aged man with the Hizbul Mujahideen group, said he used to fight against Indian forces in Kashmir but was now ready to go to Afghanistan.

"We are the reserve force," he said. "If needed I will ... take my gun, go there and fight."

Rift

The TTP publicly rubbishes any talk of a major rift among its ranks.

A Taliban spokesman has confirmed Fazlullah's appointment and said there would be no more peace talks with the government.

Operatives from Al Qaeda and the Haqqani network, a powerful militant group believed to be based in the mountains of North Waziristan, are also working hard to smooth over any disputes, sources say.

Mullah Omar, the reclusive, one-eyed leader of the Afghan Taliban, is said to have stepped into the debate and backed Fazlullah's candidacy. Fazlullah knows Omar personally, having fought alongside his men in Afghanistan in 2001.

Fazlullah is still holed up in his base in Nuristan, a thickly forested Afghan region favoured by many militants hiding from US drones. To reassert control over feuding groups he would have to come back and establish a foothold in Pakistan.

"He is a non-resident commander, he is not present physically," said a Pakistani intelligence source. "But he has two advantages: He's got a lot of money and he has Afghan support."