The latest report by Congressional Research Service (CRS) which prepares reports to the US Congress has confirmed that Pakistan was expanding its nuclear development.
The report said , "Pakistan's nuclear arsenal consists of approximately 60 nuclear warheads. It continues fissile material production for weapons, and is adding to its weapons production facilities and delivery vehicles." The report also said that Pakistan stores its warheads unassembled with the fissile core separate from non-nuclear explosives.
Admiral Mike Mullen, chairman of the US Joint Chief of Staff at a congressional meeting on May 14 has confirmed that the US has 'evidence' that Pakistan is developing its nuclear arsenal.