The latest report by Congressional Research Service (CRS) a research wing of the US Congress which prepares reports for lawmakers comes a validation to recent statements and media reports that Pakistan was expanding its nuclear arsenal. "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," said the report "Pakistan's Nuclear Weapons: Proliferation and Security issues", which was released to the media on Thursday. Admiral Mike Mullen, Chairman of the U.S. Joint Chiefs of Staff, at a Congressional hearing on May 14 had said that the U.S. has "evidence" that Pakistan is expanding its nuclear arsenal. A similar report was also published in The New York Times early this month. Pakistan stores its warheads unassembled with the fissile core separate from non-nuclear explosives, and these are stored separately from their delivery vehicles, it said. Pakistan does not have a stated nuclear policy, but its "minimum credible deterrent" is thought to be primarily a resistance to conventional military action by India. "Deterring India's nuclear weapons and augmenting Pakistan's inferior conventional forces are widely believed to be the primary motivation for Islamabad's nuclear arsenal," the CRS said. The report further states that Islamabad gained technology from many sources including uranium enrichment technology from Europe and blueprints for a small nuclear weapon and missile technology from China. Pakistan's nuclear warheads use an implosion design with a solid core of highly enriched uranium, about 15-20 kg per warhead and "Islamabad continues to produce about 100 kg of highly enriched uranium for weapons every year," the report said. Referring to expansion of Khushab plutonium production reactor by adding two additional heavy water reactors with Chinese help the report said: "the continued expansion of the complex and production of weapons materials could indicate plans to increase its nuclear weapons arsenal in near future." The CRS said even as Pakistani officials have maintained that they have already determined the arsenal size needed for minimum nuclear deterrence and they will not engage in an arms race with India, all indications were otherwise.