Pyongyang making ‘very serious’ progress on producing weapons, with rapid rise in activity at main nuclear complex

North Korea has made “very serious” progress in its ability to produce more nuclear weapons, the head of the UN’s nuclear watchdog has said, in another sign that the regime is seeking to use its nuclear arsenal to ensure its survival.

North Korea is thought to have assembled about 50 nuclear warheads, although some experts are sceptical of its claims that it is able to miniaturise them so they can be attached to long-range ballistic missiles.