Recent American and South Korean intelligence reports speculate that North Korea may be preparing for its first nuclear tests since 2009. Satellite images show that North Korea has dug an 800 metre tunnel at its test site at Punggye-ri. Experts believe that the tunnel will be ready for a nuclear test when it reaches 1 kilometre, which South Korea believes may occur in early April.

Adam Dempsey, Research Associate for the UK Defence Forum, has recently undertaken a study of North Korea's nuclear weapons programme. His report outlines the development of Pyongyang's programme and ballistic missile capabilities.

In keeping with many aspects of North Korean life, Pyongyang's nuclear weapons programme is shrouded in secrecy and subject to speculation. Official estimates of North Korea's programme are varied and remain primarily reliant on open-source intelligence. To complicate matters, Pyongyang's nuclear missile development may have benefitted from illegal exchanges involving the A.Q. Khan network.

Adam's full report is available here.