North Korea says its main reactor used for fuel for nuclear weapons is once more fully operational.
The Yongbyon plant was shut down in 2007 as part of a confidence-building exercise with the West.
An official says they are ready “at any time” to use nuclear weapons against hostile countries.
State news agency KCNA says the North is improving its nuclear weapons both in “quality and quantity” at Yongbyon.
It is the source of weapons-grade plutonium for the country’s military programme.
Satellite or missile?
The news agency also reports that Pyongyang is preparing to launch a new long-range rocket.
Critics speculate that this could carry a missile. However, the North insists it is for a satellite.
Tension remains along the border with South Korea.
Some say the nuclear news will worsen relations with the rest of the world.
But others think it could be an attempt to restart a dialogue leading to a possible easing of sanctions.