ISLAMABAD: President Asif Ali Zardari said Pakistan was battling for its "sovereignty" a day after scores of people were killed amid an escalating offensive against the Taliban.

Zardari said Pakistan would fight "until the end," as US defence officials in Washington confirmed that Islamabad plans to step up its offensive against militants in the country's troubled northwest.

"We are fighting a war for our sovereignty," Zardari said in a television address. "We will continue this war until the end, and we will win it at any cost.

"The Taliban are the enemies of innocent people. They want to terrorise the people and to take control of the country's institutions."

Zardari's pledge came after suicide bombings targeting Friday prayers at two mosques killed at least six people, including a prominent Muslim cleric, and wounded more than 100.

The bombings confirmed fears that Taliban militants are avenging an offensive against them in the northwest, where the military said Friday 39 insurgents and 10 soldiers had been killed in fresh fighting.

Religious scholar Sarfraz Naeemi, who had spoken out against Taliban suicide bombings, was among two people killed in one of the mosque attacks, in the eastern city of Lahore, police said.

Lahore police chief Pervez Rathore said a suicide bomber had entered the room where Naeemi was sitting with others after Friday prayers, and blew himself up.

Naeemi had issued a fatwa (edict) against suicide bombings carried out by Taliban militants.

In the other attack, four people died and at least 105 were wounded when an explosives-filled car ploughed into a mosque in the northwestern garrison town of Nowshera, police said.

The roof of the mosque caved in after the blast and a number of people were trapped under the rubble, police official Imran Kishwar told AFP, adding that the death toll could rise.

A spokesman for militant leader Baitullah Mehsud's Tehreek-e-Taliban Pakistan (TTP) claimed responsibility for the mosque attacks, and Tuesday's bombing of Peshawar's Pearl Continental hotel that killed nine people.

"Anyone who will oppose us to please the Americans will face the same fate," Maulvi Omar told AFP by telephone from an undisclosed location.

In Washington, senior defence officials, speaking to reporters on condition of anonymity, said Islamabad planned to step up its offensive against Taliban forces in the northwest tribal area of South Waziristan.

Confirming rumours so far denied by the Pakistani army, one of the officials said that, in addition to the major offensive in the northwest Swat valley, Pakistan is planning "a separate campaign in South Waziristan."

The region is a stronghold for the TTP, Pakistan's umbrella Taliban organisation, as well as for Al-Qaeda and other extremist groups.

The TTP will be the primary target for the increased operations, the defence official said, but the United States hopes the offensive will also put pressure on Al-Qaeda and the Afghan Taliban, who were driven out of Afghanistan and into the region after the 2001 US-led invasion.

These groups are clearly interconnected, the official said, so "an offensive certainly can play an important role," noting that the strategy is to "have pressure on both sides of the border."

A 90,000-strong US and international coalition is fighting the Afghan Taliban and other insurgents on the Afghanistan side.

A second US defence official told reporters the Pakistani army has been redeploying forces to areas surrounding South Waziristan: "We think the initial phase of the operation has already begun," the official said