As the insurgency of the Taliban and Al-Qaeda spreads in Pakistan, senior American officials are increasingly concerned about new vulnerabilities for Pakistan's nuclear arsenal, the New York Times reported on Monday.
Their concerns include the potential for militants to snatch a weapon in transport or to insert sympathisers into laboratories or fuel-production facilities, the influential US daily said citing unnamed officials.
The officials, it said, emphasised that there was no reason to believe that the arsenal, most of which is south of the capital, Islamabad, faced an imminent threat.
But the United States does not know where all of Pakistan's nuclear sites are located, and its concerns have intensified in the last two weeks since the Taliban entered Buner, a district 60 miles from the capital, the Times said.
The spread of the insurgency has left American officials less willing to accept blanket assurances from Pakistan that the weapons are safe, it said.
Pakistani officials have continued to deflect American requests for more details about the location and security of the country's nuclear sites, the officials cited by the Times said.
Some of the Pakistani reluctance, they said, stemmed from longstanding concern that the United States might be tempted to seize or destroy Pakistan's arsenal if the insurgency appeared about to engulf areas near Pakistan's nuclear sites.
Several current officials cited by the Times said that they were worried that insurgents could try to provoke an incident that would prompt Pakistan to move the weapons, and perhaps use an insider with knowledge of the transportation schedule for weapons or materials to tip them off.
That concern appeared to be what Secretary of State Hillary Clinton was hinting at in testimony 10 days ago before the House Appropriations Committee, it said. Pakistan's weapons, she noted, "are widely dispersed in the country".
"There's not a central location, as you know," she added. "They've adopted a policy of dispersing their nuclear weapons and facilities."
She went on to describe a potential situation in which a confrontation with
India could prompt a Pakistani response, though she did not go as far as saying that such a response could include moving weapons toward India - which American officials believed happened in 2002, the Times noted.