Taliban militants said Monday their peace deal with the Pakistani government was "worthless" after authorities deployed helicopters and artillery against hide-outs of Islamist guerrillas seeking to extend their grip along the Afghan border.

A collapse of the pact would likely please Obama administration officials pressing Islamabad hard for more robust action against extremists threatening Pakistan's stability and U.S. and NATO troops in neighboring Afghanistan.

President Asif Ali Zardari called for more foreign support for cash-strapped Pakistan to prevent any danger of its nuclear arsenal falling into the hands of al-Qaida and its allies.

In another sign of mounting Western concern, British Prime Minister Gordon Brown was due in Pakistan for talks on topics including cooperating against international terrorism, the British Embassy said.

Zardari also said Pakistani intelligence thought Usama bin Laden — recently offered sanctuary by militants in the area covered by the peace pact — might be dead, but said there was no evidence of the Al Qaeda chief's demise.

"He may be dead. But that's been said before," Zardari told a group of reporters. "It's still between fiction and fact."

The government agreed in February to impose Islamic law in Swat and surrounding districts that make up Malakand Division if the Taliban there would end their violent campaign in the one-time tourist haven.

In recent days, Taliban forces from Swat began entering Buner, a neighboring district just 60 miles from the Pakistani capital.

American officials have described the pact as a capitulation and urged Pakistani leaders to switch their security focus from traditional foe India to violent extremists inside their borders.

Pressure on the creaking peace deal grew further Sunday when authorities sent troops backed by artillery and helicopter gunships to attack Taliban militants in Lower Dir, part of the region covered by the pact.

Paramilitary troops killed 20 suspected militants Monday, and a total of 46 have died since the operation began, an army statement said. Maulvi Umar, a spokesman for the umbrella group of Pakistan's Taliban, claimed that insurgents in Dir had killed nine troops and lost two of their own.

Some terrified residents have fled the area clutching no more than their children and a few belongings. At least one soldier was killed Sunday.

A spokesman for the Taliban in their Swat Valley stronghold denounced the operation as a violation of the pact and said their fighters were on alert and waiting to see if a hard-line cleric who mediated the deal pronounced it dead.

"The agreements with the Pakistan government are worthless because Pakistani rulers are acting to please Americans," Muslim Khan, spokesman for Taliban militants in the Swat Valley, told The Associated Press.

A spokesman for Sufi Muhammad said the cleric was trapped in his home in the same area of Lower Dir attacked by troops and that his supporters have been unable to contact him.

"We will not hold any talks until the operation ends," spokesman Amir Izzat Khan said.

Umar , the Pakistani Taliban spokesman, said the militants would agree to talks about the situation in Dir, but only if the military operation is halted.

"We were living peacefully in Dir," Umar said. "Nothing warranted the operation."

Dianne Feinstein, head of the U.S. Senate Intelligence Committee, said Sunday that the recent Taliban advance in Buner — and the lack of a robust military response — suggested Pakistan was "in very deep trouble."

"This thing has to get sorted out and sorted out quickly or you could lose the government of Pakistan, and Pakistan is a nuclear power and that concerns me deeply," Feinstein said on CNN television.

But Pakistan's foreign minister asked U.S. officials Monday to "not panic."

"We mean business, and if we have to use force we will use force. We will not hesitate," Shah Mahmood Qureshi told The Associated Press on the sidelines of meetings with his Afghan and Iranian counterparts. "We will not surrender, we will not capitulate, and we will not abdicate."

Zardari, who has termed Pakistan's dire situation as an opportunity to draw in economic and military assistance, insisted Pakistan's nuclear weapons were in "safe hands," but added: "If Pakistan fails, if democracy fails, if the world doesn't help democracy, then any eventuality is a possibility."

Elsewhere in the northwest Monday, a remote-controlled bomb exploded near a police patrol, killing an officer and a passer-by while wounding five other police, officials said. The blast occurred near a railway crossing in the Lakki Marwat area, said Amir Ahmed, a local police officer.