North Korea has restarted a nuclear reactor widely believed to be capable of producing weapons-grade plutonium, according to a report from the global nuclear watchdog released Sunday.
The International Atomic Energy Agency said it had first spotted activity at the 5-megawatt Yongbyon plant north of the capital, Pyongyang, in late 2018 and had seen new signs of activity in recent weeks.
"Since early July 2021, there have been indications, including the discharge of cooling water, consistent with the operation," according to the report, which is issued annually and was released Sunday.
It added that the country's nuclear activities continue to be a cause for serious concern."
North Korea's leader, Kim Jong Un, has long been vocal about his nuclear ambitions, saying in January that he would seek "completely new nuclear capabilities aimed at attaining the goal of modernization of the nuclear force." Last year, he spoke of developing a "new strategic weapon."
According to the report, there have been five North Korean nuclear tests since 2006, most recently in 2017, when the U.N. Security Council demanded that the country immediately abandon its nuclear program in a "complete, verifiable and irreversible manner."
While inspectors haven't had access to North Korea since 2009 and have to rely on commercial satellite imagery to make their assessments, the new IAEA report made clear Kim's regime has not followed the Security Council's instruction.
At a 2019 summit in Vietnam with then-U.S. President Donald Trump, Kim offered to dismantle Yongbyon in exchange for relief from a range of international sanctions over nuclear weapons and ballistic missile programs.
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At the time, Trump said he rejected the deal because Yongbyon was only one part of North Korea’s nuclear program, and was not enough of a concession.
President Joe Biden's administration has said it has contacted North Korea to offer talks, but Pyongyang said it would not negotiate without a change in policy by the U.S.
"There has been no agreement governing these facilities for a long time now," Joshua Pollack, a researcher at the James Martin Center for Nonproliferation Studies, told Reuters.
In June, the IAEA flagged indications of possible reprocessing work at Yongbyon to separate plutonium from spent reactor fuel that could be used in nuclear weapons.
In the new report, the agency said the duration of that apparent work, from mid-February to early July, suggested a full batch of spent fuel was handled, in contrast to the shorter time needed for waste treatment or maintenance.
There were also indications of mining and concentration activities at a uranium mine and plant at Pyongsan and activity at a suspected covert enrichment facility in Kangson, it added.
It is a safe bet that North Korea intends any newly separated plutonium for weapons, Pollack said, adding that in a speech this year Kim gave a long list of advanced weapons under development, including more nuclear bombs.
"North Korea’s appetite for warheads is not yet sated, it seems."