Pakistan is building 20 nuclear bombs a year and could become the world's third-largest nuclear power within a decade, according to a new report.
The U.S.-based Carnegie Endowment for International Peace and the Stimson Center say Pakistan could possess at least 350 nuclear warheads. Only the United States and Russia would have more.
The report cites Pakistan's perceived need to keep pace with arch rival India.
"If deterrence fails, it appears that Pakistan has no intention of losing a nuclear war with India," the report stated.
But it said Pakistan would pay a high price for its aggressive nuclear buildup.
"With a growing population, major social and education requirements, severe energy shortfalls ... as well as requirements to bolster law enforcement and a judiciary ... Islamabad can ill afford nuclear mortgage payments that will balloon in the decades ahead," it said.
Pakistan has not yet responded to the report.
A State Department spokesman said that while U.S. officials were still going through the report, they urged Pakistan and all nuclear states to exercise restraint.
India and Pakistan, which have fought three wars, declared themselves nuclear powers in 1998, and relations between the countries remain extremely tense.
India has promised never to launch a first nuclear strike, but Pakistan has so far declined to follow.