As the Taliban extended the Pakistani territory under their control in recent months, U.S. officials have warned of a severe threat to global security unless Pakistan's government takes a tougher line.
Following are some key quotes from officials:
"I am very comfortable that nuclear weapons in Pakistan are secure."
-- Admiral Mike Mullen, chairman of the Joint Chiefs of Staff, Pentagon news conference, February 2, 2008
"I'm reasonably comfortable that the nuclear weapons are secure."
-- Mullen, speaking at Hudson Union Club, April 3, 2009
"I'm confident that we can make sure that Pakistan's nuclear arsenal is secure, primarily, initially, because the Pakistani army, I think, recognizes the hazards of those weapons falling into the wrong hands."
-- U.S. President Barack Obama, White House news conference, May 1, 2009
"Pakistan ... I think poses a mortal threat to the security and safety of our country and the world ...
"We cannot underscore (enough) the seriousness of the existential threat posed to the state of Pakistan by the continuing advances, now within hours of Islamabad, that are being made by a loosely confederated group of terrorists and others who are seeking the overthrow of the Pakistani state, which as we all know is a nuclear-armed state."
-- U.S. Secretary of State Hillary Clinton, testimony to House of Representatives Foreign Affairs Committee, April 22, 2009
"Pakistan has 173 million people, 100 nuclear weapons, an army bigger than the U.S. Army, and al-Qaeda headquarters sitting right there in the two-thirds of the country that the government doesn't control..
"We're now reaching the point where within one to six months we could see the collapse of the Pakistani state, also because of the global financial crisis, which just exacerbates all these problems ...
"The collapse of Pakistan, al-Qaeda acquiring nuclear weapons, an extremist takeover -- that would dwarf everything we've seen in the war on terror today."
-- David Kilcullen, Australian anti-insurgency expert and adviser to General David Petraeus, head of U.S. Central Command, in a Washington Post interview in March.
"Pakistan has taken important steps to safeguard its nuclear weapons, though vulnerabilities exist ...
"Al Qaeda continues efforts to acquire chemical, biological, radiological or nuclear (CBRN) materials and would not hesitate to use such weapons if the group develops sufficient capabilities."
-- General Michael Maples, director of the Defense Intelligence Agency, testimony to Senate Armed Services Committee, March 10, 2009.
(Compiled by Andrew Marshall; Editing by Jerry Norton)