ISLAMABAD - The Pakistani Taliban say they will resist until the "last breath" as security forces entered two militant-held towns and fought on the outskirts of a third in what could turn into bloody urban battles near the Afghan border.

As Pakistani political leaders gathered Monday to discuss the military operation in the Swat Valley and surrounding areas, the prime minister insisted the country's nuclear arsenal is safe, comments that follow reports it is expanding its nuclear stockpile.

Washington has pressed Islamabad to crack down on al-Qaida and Taliban strongholds along the Afghan frontier, saying the militants threaten not only U.S. and NATO troops in Afghanistan but also Pakistan's existence.

A top official said Sunday the military offensive had killed more than 1,000 suspected militants and would proceed until the last insurgent is "flushed out." Taliban spokesman Muslim Khan said later in the day the militants were defiant.

"We will fight until the last breath for the enforcement of Islamic law," Khan said in a brief phone call from an undisclosed location.

"We consider ourselves on the right path."

Swat was once a tourist destination that fell prey to Taliban advances over the last two years. The military's latest offensive in the region has already led to an exodus of nearly one million people. About 100,000 of them are now in sweltering refugee camps.

The battle in Swat's towns in particular could prove a stiff test for Pakistan's military.

The army is geared toward fighting a conventional battle against longtime rival India on the plains of the Punjab region using tanks and artillery and it has limited experience battling guerrillas in urban settings.

The military has tried operations in Swat before but failed to force out the Taliban, many of whom could blend in easily with the regular population or had hideouts in the mountains. Civilians in Swat said the military's heavy use of air strikes killed many innocents instead of militants.

In a statement Sunday afternoon, the army said 25 militants and a soldier died in the previous 24 hours of the operation.

Security forces engaged in firefights with militants on the outskirts of Swat's main town Mingora, where many of the estimated 4,000 Taliban fighters in the valley are believed to be holed up, the statement said.

It also said security forces had surrounded and entered the towns Matta and Kanju to take on the militants and it requested civilians still in those areas stay away from the Taliban hideouts.

Troops were making gains in the remote Piochar area, the rear base of Swat Taliban leader Maulana Fazlullah, it added.

Army spokesmen reached Monday morning said they had no new updates.

Pakistan's weak civilian government has been trying to rally public support behind the offensive and it has done relatively well - something made easier by public anger over Taliban advances into a district just 100 kilometres from the capital Islamabad.

News channels have been broadcasting spots such as one featuring ordinary Pakistanis saluting the army, while a variety of groups have collected funds and goods to send to the displaced civilians.

To get more consensus, government officials met with the leaders of all the major political parties Monday in Islamabad.

At the start of the mostly private session, Prime Minister Yousuf Raza Gilani said the army would stay in Swat until the displaced can safely return but warned there must be a political solution in the long run.

Admiral Mike Mullen, the chairman of the U.S. joint chiefs of staff, told a congressional panel last week there is evidence Pakistan is adding to its nuclear weapons systems and warheads. Without directly mentioning the reports, Gilani sought to allay fears.

"I want to tell the world in categoric terms that with the blessing of God, Pakistan's nuclear assets are safe and it will remain safe and anyone, no matter how powerful and influential, eyeing on our national assets will not succeed," Gilani said.

Interior Minister Rehman Malik gave the 1,000-plus militant death toll Sunday but it was not possible to independently verify it. The territories bombarded over the last three weeks are now too dangerous for journalists to freely roam.

The army also hasn't explained how it is differentiating militant deaths from civilian ones. It hasn't given a civilian death toll. Accounts from witnesses and doctors suggest dozens of civilians have been killed or wounded.

The military also did not detail how many ground troops were involved in the latest advances.