Pakistan was mobilising troops and artillery today to launch a massive offensive against Baitullah Mehsud, the leader of the Pakistani Taleban, in his mountain stronghold of South Waziristan — also believed to be the hiding place of Osama bin Laden.

Military officials told The Times that the Government had ordered the attack and the military was pounding Mr Mehsud’s territory with heavy artillery and airstrikes and negotiating alliances with rival tribal leaders in preparation for a ground assault.

They also said that the army — already fighting the Taleban in Swat and several other parts of northwestern Pakistan — was engaged in its biggest military operation since the 1971 war that split Pakistan and created Bangladesh.

The army has given no schedule for the new attack, but locals reported seeing troop columns moving towards South Waziristan. Analysts say that they expect the army to capitalise on its high levels of public support and launch its offensive within the next few weeks. “For the last few days, thousands of security forces with reinforcements of tanks and artillery are being shifted there,” one local intelligence official said. “It’s the first time in history we have seen and heard about such a big military movement into South Waziristan.”

Zahiruddin Khan, 25, a shop owner in the town of Tank, just outside South Waziristan, said he had seen army convoys heading towards the region and many families fleeing in the opposite direction in the past few days.

That will be welcome news for the United States, which has been pushing the Pakistani Army for years to take on Taleban and al-Qaeda fighters sheltering in North and South Waziristan, both of which border Afghanistan.

Some concerns have been raised that the new assault might overstretch the army before it has consolidated recent gains in the offensive it launched against the Taleban in Swat in late April. Aid workers also worry that it will create another 500,000 refugees, adding to the 2.5 million who have already fled fighting in the northwest in the last year. “If that happens you have the makings of a very serious problem indeed,” said Shaheen Chughtai, of Oxfam in Pakistan.

The Government gave the order to attack Mr Mehsud after he claimed responsibility for a spate of suicide bombings in revenge for the Swat operation. “Baitullah Mehsud is the root cause of all evils,” said Owais Ghani, the Governor of North West Frontier Province. Major-General Attar Abbas, the army spokesman, said that the exact timing of the operation, the number of troops and other details were still being worked out.

Military sources said that the aim would be to kill or capture Mr Mehsud and his key lieutenants as they posed the greatest threat to Pakistan. Mr Mehsud, who has a $5 million (£3 million) US bounty on his head, is also blamed for the assassination of Benazir Bhutto, the former Prime Minister and late wife of Asif Ali Zardari, the President.

Mr Mehsud leads Tehrek-e-Taleban Pakistan — also known as the Pakistani Taleban — and is believed to have 10,000 to 20,000 men under his command, mostly from the Mehsud tribe. Under US pressure, the army has launched several offensives against him and other militant leaders in North and South Waziristan since 2004, but each has ended in a short-lived peace deal.

When the army attacked Mr Mehsud last year it stopped because of fears of civilian casualties and because he had surrounded a fort with about 300 Pakistani troops inside.

The army is also hoping that the US will provide night vision equipment for its fighter jets and attack helicopters in time for the operation.

With or without that support, analysts say that the fighting in South Waziristan will be far fiercer than in Swat, as the former has been controlled by the militants for most of the past eight years.

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