North Korea could have doubled its stockpile of nuclear weapons in the last 18 months, a US research institute has claimed. Kim Jong-un may have added six or more weapons by significantly expanding the Stalinist nation’s nuclear weapons production, according to the Washington-based Institute for Science and International Security (ISIS).

The theory is based on an analysis of the country’s production of weapons-grade uranium and plutonium recovered from spent nuclear fuel. North Korea had an estimated 10 to 16 nuclear weapons at the end of 2014. In revised estimates contained in a report provided to Reuters, the institute’s David Albright and Serena Kelleher-Vergantini said North Korea may have added another four to six weapons since then, for a total of 13 to 21 or even more today. READ MORE