A pro-government tribal leader opposed to the Taleban chief Baitullah Mehsud was shot dead today, dealing a serious blow to the Pakistani military's offensive against the militants in the lawless tribal region bordering Afghanistan.

Qari Zainuddin, the leader of a rival faction of Mr Mehsud’s tribe inhabiting the troubled South Waziristan region, was shot dead in his house in Dera Ismail Khan by a lone gunman, who escaped after firing.

The murder came as the military prepares an offensive against Mr Mehsud, who has been accused of a string of bomb attacks, including the assassination of Benazir Bhutto, the former Prime Minister, in 2007.

Baz Mohammad, an aide of the militant commander who was also wounded, alleged that a guard had barged in to a room at Mr Zainuddin's compound after morning prayers and opened fire. He vowed to avenge Mr Zainuddin’s death.

Mr Zainuddin had publicly supported the military operation against Mr Mehsud. He had presented himself as a more moderate tribal commander, denouncing the terrorist attacks allegedly sponsored by Mr Mehsud.

"Whatever Baitullah Mehsud and his associates are doing in the name of Islam is not a jihad, and in fact it is rioting and terrorism," Mr Zainuddin said in a recent interview.

Analysts said that Mr Zainuddin's murder was a serious blow to the military campaign against the militants, as support of his faction was considered crucial. "[It] is a warning to other pro government tribal commanders," said Mahmood Shah, a retired brigadier who had served as top official in the tribal region.

Pakistan mounted a military offensive against Mr Mehsud this month in South Waziristan which is suspected to be the centre of the terrorism that has rocked the country.

Pakistani and Western intelligence agencies believe that the region bordering Afghanistan is also the base of al-Qaeda activities and the hiding place of Osama bin Laden.

General Ashfaq Kayani, the chief of the Pakistani Army, said that the main objective of the recent military operation was to eliminate Mr Mehsud.

Pakistani air force jets have been bombing Makin, a Taleban stronghold. Yesterday at least 21 people were killed in air strikes in South Waziristan. Residents said some civilians were also among the dead.

A military spokesman said that the security forces had secured a main supply route in the region and were closing in on Mr Mehsud's stronghold.

Earlier today three missiles fired by a US predator in the Ladha district in South Waziristan, killed at least six people.

Security sources said that the missiles were fired after the assassination of Mr Zainuddin, and hit compounds of the supporters of Mr Mehsud. It was the third US drone attack on Mr Mehsud's stronghold.

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