The Pakistani Army faced resistance from the Taleban on the second day of an assault on the mountainous tribal region of South Waziristan yesterday, raising fears of a drawn-out battle.

The army said that it had made significant advances and killed at least 60 militants in the first 24 hours of the long-awaited ground offensive on a region considered to be the main Taleban and al-Qaeda stronghold in Pakistan.

Residents and local officials from the area on the Afghan border said that the insurgents were attacking military convoys as they advanced from three directions on the area controlled by Hakimullah Mehsud, the Taleban leader. “They have sophisticated weapons and are trying to block the troops’ advance,” a local reporter in Wana, the regional headquarters, said.

The Taleban said that it repelled the attack, inflicting heavy casualties but losing only one of its fighters.

Azam Tariq, a spokesman for the Taleban, said: “The Government has put the country’s sovereignty at stake to please Obama . . . we’ll attack his well-wishers everywhere.”

About 30,000 army troops, backed by fighter jets and helicopter gunships, began the assault on Saturday. They aim to kill or capture Mr Mehsud and his followers, who have been blamed for attacks across Pakistan in the past fortnight.

Mr Mehsud took over the leadership of the Taleban after his brother, Baitullah Mehsud, was killed by a US drone strike in August. He appears to be working with al-Qaeda and militant groups in Punjab province.

Major-General Athar Abbas, the army spokesman, said that 80 per cent of recent militant attacks emanated from South Waziristan, and that Western intelligence agencies considered it to be the main al-Qaeda base.

“It is the most critical battle for the military,” he said. “We cannot eliminate militancy without destroying their main sanctuaries in South Waziristan.”

The army has been moving troops into the region since the Government announced the operation in June. They have blocked roads and pounded militant hideouts with air raids and artillery fire.

A senior army officer told The Times that the “last straw” was an attack on the army headquarters in the garrison town of Rawalpindi nine days ago.

The army is up against 10,000 trained and well-armed local militants and about 2,000 foreign fighters, mostly from Central Asia.

The insurgents control about 1,275sq miles (3,302sq km) of territory, or about half of South Waziristan, which has a population of 250,000.

Fighting in Sarwaki yesterday killed one soldier and seven insurgents. Five more soldiers were killed elsewhere.Analysts said that military casualties were likely to rise in the coming week as troops advance into rugged terrain. Thousands of civilians have been leaving the conflict zone in open-top vans piled high with their belongings. About 100,000 fled before the offensive began and up to 16,000 came out in the past few days.

The military said that it would take six to eight weeks to clear the area of insurgents. Some defence analysts said that it could take longer because of the hostile terrain and the army’s previous record in the region.

In 2004 and 2008 the army moved into South Waziristan, but on both occasions was forced to pull back and sign peace deals with the insurgents.Military officials admitted that those agreements had, in effect, turned the region into a hub for al-Qaeda and Taleban militants, who were involved in cross-border attacks on Nato forces in Afghanistan. This time they are determined to hold the territory.

“This time we are going in with sufficient troops not to let the militants come back,” General Abbas said.

The offensive follows a successful assault in the spring on the Swat Valley, which had fallen under the Taleban’s control. That operation earned praise from Western countries, raising the morale of Pakistani troops.

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