Pakistan is expanding its nuclear arsenal and has developed an estimated stockpile of 130 to 140 warheads for delivery as well as converting some of its fighter jets, including F-16s to deliver nukes, Bulletin of Atomic Scientists said in its latest report.

"Speculation that Pakistan may become the world's third-largest nuclear weapon state - with a stockpile of some 350 warheads a decade from now - are, we believe, exaggerated, not least because that would require a buildup two to three times faster than growth over the past two decades," it said.

"We estimate that its stockpile could more realistically grow to 220-250 warheads by 2025, if the current trend continues. If that happens, it would make Pakistan the world's fifth-largest nuclear weapon state.