North Korea appears to have reopened a plant to produce plutonium from spent fuel of a reactor central to its atomic weapons drive, the International Atomic Energy Agency (IAEA) on Monday, according to Reuters.
North Korea 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 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.
"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 was quoted as having told a news conference on Monday.
"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.
In recent months, North Korea has carried out several tests of ballistic missiles. Some of the tests have been successful, but in April, the North failed three times to test-fire a medium-range Musudan missile, and another such attempt failed last week.
North Korea has also come under tightening international pressure over its nuclear weapons program, including tougher UN sanctions adopted in March following its most recent nuclear test in January.
North Korea's ruling party congress recently formally adopted leader Kim Jong-Un's policy of developing the country's nuclear arsenal in tandem with the economy.
In a speech before the congress, Kim adopted a soft tone on his country’s nuclear program, saying the country would only use nuclear weapons if attacked by a nuclear power, adding he wanted improved relations with previously "hostile" nations.