The death of Qari Zainuddin, the rival leader, comes as a serious blow to the government, which had supported him as a counter to Mehsud in its campaign against the Taliban.

Zainuddin was killed in the northwestern town of Dera Ismail Khan, said Iqbal Khan, the town’s district police chief. The initial investigation indicated that the gunman was a guard named Gulbadin Mehsud who was thought to have been loyal to Zainuddin. The alleged attacker, who was not directly related to Baitullah Mehsud, escaped after the attack, which also wounded another guard, he said.

The military is mounting an operation against Mehsud in his sanctuary in South Waziristan, a mountainous tribal region in western Pakistan. Zainuddin and his group were helping the government by denying Mehsud and his fighters the ability to operate in a nearby region, and in recent months, killing some 30 of his fighters. Pakistani jets have also targeted Mehsud’s hideouts in recent days.

The killing showed the long reach of Mehsud, whose suicide bombings in major cities have terrorised Pakistanis for years. It was also intended as a reminder that there are serious consequences for crossing him, analysts said. Zainuddin had been a vociferous critic of Mehsud and his tactics.

“It tells people if you side with the government this is what will happen to you,” said Talat Masood, a retired general and military analyst. “It says the government can’t give you protection but the other side can.”

The killing also showed just how tenuous this splinter group’s hold on power in the Tank and Dera Ismail Khan area was, Masood said, and brings into question the government’s reliance on a strategy of dividing the Mehsud tribe in order to defeat it. The army, which is in the early stages of deploying troops to South Waziristan would now have to rely more on its own fighters, he said.

Zainuddin, who in his 30s, was part of Mehsud’s tribe, but had split with him, and joined forces with Turkestan Bhaitani, an older Taliban fighter who had switched sides to ally with the government. The two men had held a tribal meeting, with as many as a hundred elders of the Mehsud tribe in the town of Tank earlier this month in an effort to rally opposition to Mehsud. Officially, the Pakistani military denies supporting Zainuddin or Turkestan Bhaitani.

Zainuddin was the cousin of Abdullah Mehsud, a top Taliban militant who was killed in 2007 when security forces raided a hideout in Baluchistan Province. He had claimed that he had the ability to take on Mehsud with the support of 3,000 fighters. “Baitullah Mehsud is not involved in jihad because Islam does not allow suicide attacks, which his group is perpetrating,” Zainuddin was quoted as saying in one interview.