North Korea appears to have restarted a nuclear reactor that is widely believed to have produced plutonium for nuclear weapons, the UN atomic watchdog has said in an annual report.

The International Atomic Energy Agency (IAEA) has had no access to North Korea since Pyongyang expelled its inspectors in 2009. The country then pressed ahead with its nuclear weapons programme and soon resumed nuclear testing. Its last nuclear test was in 2017.

The IAEA now monitors North Korea from afar, largely through satellite imagery.

“There were no indications of reactor operation from early December 2018 to the beginning of July 2021,” the IAEA report said of the 5-megawatt reactor at Yongbyon, a nuclear complex at the heart of North Korea’s nuclear programme.

“However, since early July 2021, there have been indications, including the discharge of cooling water, consistent with the operation of the reactor.”

The IAEA issues the report annually before a meeting of its member states, posting it online with no announcement. The report was dated Friday.

The IAEA said in June there were indications at Yongbyon of possible reprocessing work to separate plutonium from spent reactor fuel that could be used in nuclear weapons.

Friday’s report said the duration of that apparent work – five months, 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.

“The new indications of the operation of the 5MW(e) reactor and the Radiochemical (reprocessing) laboratory are deeply troubling,” it said.

There were indications “for a period of time” that what is suspected to be a uranium enrichment plant at Yongbyon was not in operation, it said. There were also indications of mining and concentration activities at a uranium mine and plant at Pyongsan, it added.