North Korea appears to have reopened a plant to produce plutonium from the spent fuel of a reactor central to its atomic weapons drive, the UN nuclear watchdog says, suggesting the country's arms effort is widening.
Pyongyang vowed in 2013 to restart all nuclear facilities, including the main reactor at its Yongbyon site that had been shut down and has been at the heart of its weapons program.
It said in September that Yongbyon was operating and that it was working to improve the "quality and quantity" of its nuclear weapons. It has since carried out what is widely believed to have been a nuclear test.
The International Atomic Energy Agency (IAEA), which has no access to North Korea and mainly monitors its activities by satellite, said last year it had seen signs of a resumption of activity at Yongbyon, including at the main reactor.
"Resumption of the activities of the 5 megawatt reactor, the expansion of centrifuge-related facility, reprocessing, these are some of the examples of the areas (of activity indicated at Yongbyon)," IAEA chief Yukiya Amano told a news conference during a quarterly IAEA Board of Governors meeting on Monday.
Centrifuges are machines that enrich uranium, a process that can purify the element to the level needed for use in the core of a nuclear weapon. Reprocessing involves obtaining plutonium from spent reactor fuel, the other main route to a bomb.
"There are indications the reprocessing plant at Yongbyon has been reactivated," an IAEA spokesman said later on Monday.
"It is possible that it is reprocessing spent fuel."
Little is known about the quantities of weapons-grade uranium or plutonium that North Korea possesses, or its ability to produce either, though plutonium from spent fuel at Yongbyon is widely believed to have been used in its nuclear bombs.
North Korea has come under tightening international pressure over its nuclear weapons program, including tougher UN sanctions adopted in March backed by its lone major ally China, following its most recent nuclear test in January.