North Korea restarts plutonium reactor

Washington - North Korea has restarted a plutonium reactor that could provide fuel for nuclear weapons, US Director of National Intelligence James Clapper said on Tuesday.

"We further assess that North Korea has been operating the reactor long enough so that it could begin to recover plutonium from the reactor's spent fuel within a matter of weeks to months," he said.

North Korea mothballed the Yongbyon reactor in 2007 under an aid-for-disarmament accord, but began renovating it after its third nuclear test in 2013.

When fully operational, the reactor is capable of producing around 6kg of plutonium a year - enough for one nuclear bomb, experts say.

Last month, Washington-based think tank the Institute for Science and International Security said satellite images suggest the reactor is operating intermittently.

But Clapper said that, in the wake of North Korea's latest nuclear weapon and ballistic missile tests, the regime poses "a serious threat to US interests".