Senior American officials say they are increasingly concerned Pakistan’s nuclear arsenal may be at risk from a rising Taliban and Al Qaeda insurgency in the vulnerable country, the New York Times reported Monday.

Officials told the Times they are worried militants could take possession of the arms during transport or by potentially infiltrating atomic laboraties or fuel-production plants, but emphasized that there was no reason to believe that the arsenal faced an imminent threat.

The Taliban's recent incursion into Buner, a key region 60 miles from the capital, Islamabad, heightened global fears as the whereabouts of all of Pakistan’s nuclear sites is unknown.

According to The Times, the insurgency has left U.S. officials less willing to accept blanket assurances from Pakistan that the weapons are safe.

"We are largely relying on assurances, the same assurances we have been hearing for years," an official told the newspaper. "The worse things get, the more strongly they hew to the line, ‘Don’t worry, we’ve got it under control.’ "

Pakistanis, however, have continued to rebuff American requests for more details about the location and security of the country's nuclear sites, the report noted.

Some of Pakistan's reluctance stemmed from longstanding concern that the U.S. might be tempted to seize or destroy the nation's arsenal if the insurgency spread further, according to the paper.

The U.S. government has not yet engaged the most senior officials of the Pakistani government on the issue, but may begin this week as Preident Obama meets at the White House with Pakistani President Asif Ali Zardari on Wednesday.

Pakistan's army and the Taliban blamed each other Sunday for a rise in tensions that threatened to destroy a much-criticized peace deal.

The army accused militants in the Swat Valley of looting, attacking infrastructure and killing one soldier. A Taliban spokesman said militants will start patrolling Swat's main town, and acknowledged that they cut the throats of two soldiers as revenge for the army killing two insurgents.

What happens to the peace pact is likely to figure prominently in talks between Pakistani President Asif Ali Zardari and Obama later this week. Zardari is expected to ask for more money to help Pakistan's battered economy and under-equipped security forces.

Under February's peace deal, the government agreed to impose Islamic law in the districts that make up the Malakand Division in hopes that the militants would lay down their arms.

But the Taliban in Swat were emboldened, and soon entered the adjacent Buner district to impose their harsh brand of Islam.

Pakistan has insisted on using negotiations and force in tackling violent extremism within its borders. It's an approach that worries U.S. officials, who warn that peace deals allow the insurgents time and room to strengthen.

Taliban and Al Qaeda fighters already have strongholds along Pakistan's border regions from which to plan attacks on U.S. and NATO forces in neighboring Afghanistan, and American leaders don't want to see Swat turn into a sanctuary for them.

Sunday, the Swat Taliban started patrolling Mingora, the valley's main town, in response to military patrols, Taliban spokesman Muslim Khan said.

"We are not violating the peace deal. This is government and security forces who are doing that. We have started armed patrols in response to security forces patrols. We will keep on doing that if they do, and we wouldn't if they don't. We have a right to defend ourselves," Khan said.

In recent weeks, the militants have moved into Buner, a district just 60 miles from Islamabad. The proximity of the district to the capital raised alarms domestically and abroad, and Pakistan's military went on the offensive over the past week to drive the Taliban out.

An army statement Sunday said 80 militants including an important local commander had been killed, along with three soldiers. But the army's statement focused much more on Swat itself.

It accused militants there of looting a bank, attacking a power grid and blowing up part of a bridge. It said security forces discovered at least three explosives-laden vehicles apparently intended for suicide attacks.

The militants were "in gross violation of the peace accord" and their actions threatened "the lives of the (civilian) population, civil administration as well as security forces personnel," the army statement said.

On top of that list, two security personnel were discovered with their throats slit and their bodies and faces mutilated Sunday in Swat, a security official said on condition of anonymity because he was not authorized to talk to media on the record.

The Taliban spokesman said the men were killed in revenge for the military's killing of two insurgents.

The government ordered a curfew for Swat from 9 p.m. to 6 a.m., said Khushal Khan, an administrator who also confirmed the militant patrols. It was unclear what officials could do if the militants ignored the order.

The dangerous nature of Swat made it difficult to independently verify the army's accusations Sunday.

Even as the government and the militants hardened their positions, officials in Pakistan's northwest sought to keep the peace deal alive, insisting that the pact retains, at the very least, symbolic value.

Officials announced Saturday that they had set up an Islamic appeals court as their part of the deal. A speedier justice system has long been a demand of Swat residents, and setting up the court takes away a grievance that militants have exploited, officials say.

A cleric mediating the pact however rejected the panel.

By carrying out their part of the agreement, officials say, the government can gain more support from the public to take action against the Taliban if the militants violate the pact. Many Swat residents desperate for a stop to the fighting welcomed the deal, even if it didn't evict the Taliban.

Still, the army's harsh stance does not guarantee a return to fighting in Swat itself. Some two years of clashes between the two sides killed hundreds and displaced up to one-third of Swat's 1.5 million residents before the peace deal was crafted.

The army, which has struggled in the field of counterinsurgency, could not keep the militants from taking control of most of the valley. It's unclear that it has the capacity to defeat the Swat Taliban now or the stomach to try.

The Associated Press contributed to this report.