WASHINGTON (AFP) -- The United States has developed contingency plans to safeguard Pakistani nuclear weapons if they risk falling into the wrong hands, but U.S. officials worry that their limited knowledge about the location of the arsenal could pose a problem, The Washington Post reported Sunday.

""We can't say with absolute certainty that we know where they all are,"" the newspaper quotes an unnamed former U.S. official as saying.
If an attempt were made by the United States to seize the weapons to prevent their loss, ""it could be very messy,"" the official said.
Of the world's nine declared and undeclared nuclear arsenals, none provokes as much worry in Washington as Pakistan's, the report said.
The government in Islamabad is arguably the least stable. Some Pakistani territory is partly controlled by insurgents bent on committing hostile acts of terrorism in the West. And officials close to the seat of power -- such as nuclear engineer A.Q. Khan -- have a worrisome track record of transferring sensitive nuclear technology.
Because the risks are so grave, U.S. intelligence officials have long had contingency plans for intervening to obstruct such a theft in Pakistan, the paper said, citing ""two knowledgeable officials.""
The officials would not discuss details of the plans, but several former officials said the plans envision efforts to remove a nuclear weapon at imminent risk of falling into terrorists' hands, The Post said.
The plans imagine, in the best case, that Pakistani military officials will help the Americans eliminate that threat, according to the report.
But in other scenarios there may be no such help, said Matt Bunn, a nuclear weapons expert and former White House science official in the Clinton administration.
""We're a long way from any scenario of that kind,"" Bunn is quoted as saying. ""But the current turmoil highlights the need for doing whatever we can right now to improve cooperation and think hard about what might happen down the road.""
Former and current administration officials say they believe that Pakistan's stockpile is safe, the paper said.
But they worry that its security could be weakened if the current turmoil persists or worsens. They are particularly concerned by early signs of fragmented loyalties among Pakistan's military and intelligence leaders, The Post said.