Pakistan said it killed 60 militants and lost 11 soldiers as a 30,000-strong attack force pushed into Taliban's tribal stronghold on the second day of a major operation.

Taliban fighters offered fierce resistance as ground troops, backed by warplanes and artillery, pushed into South Waziristan, the mountain headquarters of the notorious Tehrik I Taliban Pakistan (TTP).

Militants detonated roadside bombs and opened fire on helicopter gunships. Villagers, some of them women, waved white flags and troops searching houses discovered large weapons caches, the military said.

In a statement it said tactical heights near Razmak, a mountain village at the northern edge of South Waziristan, had been captured following fighting that killed 10 militants and two soldiers.

The Taliban denied the army claims, and a spokesman insisted the guerrillas had inflicted "heavy casualties" and forced the invading soldiers back into their bases. "We know how to fight this war and defeat the enemy with the minimum loss of our men," Azam Tariq told the Associated Press from an undisclosed location.

The conflicting versions were impossible to reconcile. Inaccessible at the best of times, much of South Waziristan has been sealed off since the operation started on Saturday morning. Phone connections to Waziristan and nearby areas have been disconnected.

The fight, pitting 30,000 soldiers against 10,000 Taliban and al-Qaida miltants, according to the army, followed two weeks of audacious assaults in cities that left over 175 people dead and underlined the militant threat to national stability.

In the most shocking incident, a team of 10 gunmen laid siege to the army headquarters in Rawalpindi for 22 hours. All but one were killed. The army said the attack was orchestrated from South Waziristan.

The army has surrounded a mountainous swath of South Waziristan that is controlled by the Mehsud tribe, whose most notorious member, Baitullah Mehsud, was killed by a US drone last August. Mehsud's successor as leader, Hakimullah Mehsud, vowed to take revenge, apparently triggering the recent wave of militant attacks.

The military operation, which has been in the offing since June, has caused more than 110,000 people to flee their homes. Authorities expect another 140,000 to join them.

Soldiers are attacking the Mehsud territory from Razmak in the north, Jandola in the east and Wana in the south. Officials estimate the drive will take a minimum of six weeks and could stretch through the winter. The non-Mehsud parts of South Waziristan, which are controlled by the rival Wazir tribe and border with Afghanistan, have not been affected.

The army hopes to repeat the success of its campaign against the Taliban in Swat this summer. But few doubt this operation will be harder, longer and with a great risk of failure.

Riffat Hussain, a defence analyst, said the army's goal was to "degrade" the capability of the Taliban to launch attacks from Waziristan, and to kill an estimated 800 to 1,500 foreign fighters – mainly from Uzbekistan – sheltering in the area.

The al-Qaida-allied Uzbeks fled to Waziristan after 2001 and have become "naturalised citizens" through marriages with local women and the provision of training and finance to local militants.

"The core objective is to kill as many of the foreign militants who are also sympathisers of al-Qaida as possible," said Hussain. "They have no place to go, they know the area well and are highly motivated. That's a lethal combination."

The border area has a reputation as the graveyard of empires and Pakistan's army has had little more success in recent years. Three peace deals with Taliban militants in Waziristan between 2004 and 2006 failed badly, emboldening the militants to extend their violent campaign across North-West Frontier province.

This time, the army says, it is no longer prepared to talk. But the generals have made tactical compromises that leave western allies uncomfortable. In order to encircle the Mehsud area, the army has struck fragile agreements with rival militant groups controlled by Maulvi Nazir, in South Waziristan, and Hafiz Gul Bahadur, in North Waziristan. Although less famous than the Mehsud-led TTP, both warlords dispatch significant numbers of Taliban fighters to attack Nato forces across the border in Afghanistan.

The Mehsud territory of South Waziristan, in contrast, does not share a border with Afghanistan, and the Taliban based there have concentrated their firepower inwards on Pakistan.