North Korea says it will restart all facilities at its main Yongbyon nuclear complex, including a reactor mothballed in 2007.
In a statement, it said the move would bolster North Korea’s nuclear forces “in quality and quantity”.
The move is the latest in a series of measures by Pyongyang in the wake of its third nuclear test in February.
It has been angered by the resultant UN sanctions and joint US-South Korea annual military drills.
In recent weeks the communist state has issued a series of threats against both South Korean and US targets, to which the US has responded with high-profile movements of advanced aircraft and warships around the Korean peninsula.
A South Korean foreign ministry spokesman said that if true, the North Korean move would be “highly regrettable”.
Chinese foreign ministry spokesman Hong Lei called for restraint from all sides to resolve the “complex and sensitive” situation.
Delivered by The Daily Sheeple
We encourage you to share and republish our reports, analyses, breaking news and videos (Click for details).
Contributed by BBC of bbc.co.uk.