North Korea, which conducted its fourth nuclear test in January, vowed in 2013 to restart all nuclear facilities, including the main reactor and the smaller plant at Yongbyon, which was shut down in 2007 as part of an international disarmament-for-aid deal that later collapsed. Photograph: Getty Images

North Korea has restarted production of plutonium fuel, a senior US state department official said on Tuesday, showing that it plans to pursue its nu(...)