North Korea’s UN envoy said his country was not bound by the non-proliferation treaty (NPT) on nuclear weapons and external pressure would not change its status as a nuclear-armed state, official media reported on Thursday. Pyongyang threatened to withdraw from the treaty in 1993 and formally did so in 2003. It has since conducted six nuclear tests – prompting a raft of international sanctions – and is believed to possess dozens of nuclear warheads. Signatories of the NPT have been holding a...