NORTH KOREA APPEARS to have restarted the operation of its main nuclear reactor used to produce weapons fuels, the UN atomic agency said.

The annual report by the International Atomic Energy Agency (IAEA) refers to a 5-megawatt reactor at the country’s main nuclear complex in Yongbyon, north of Pyongyang.

The reactor produces plutonium, one of the two key ingredients used to build nuclear weapons along with highly enriched uranium.

The report said: “Since early July 2021, there have been indications, including the discharge of cooling water, consistent with the operation of the reactor.”

It added there were indications of the operation of Yonbyon’s radiochemical laboratory from mid-February to early July this year.

The report said this period of operation is consistent with previous reprocessing campaigns announced by North Korea of irradiated fuel discharged from the reactor.

The laboratory is a facility where plutonium is extracted by reprocessing spent fuel rods removed from reactors.

The IAEA said: “(North Korea’s) nuclear activities continue to be a cause for serious concern. Furthermore, the new indications of the operation of the 5-megawatt reactor and the radiochemical laboratory are deeply troubling.”

The IAEA has not had access to Yongbyon or other locations in North Korea since the country kicked out IAEA inspectors in 2009. The agency said it uses satellite imagery and open source information to monitor developments in North Korea’s nuclear programme.

The Yongbyon complex also produces highly enriched uranium, the other key nuclear fuel.

The IAEA report said “there were indications, for a period of time, that the reported centrifuge enrichment facility was not in operation” though regular vehicular movements were observed.

The complex, which North Korea calls “the heart” of its nuclear programme and research, has been at the centre of international concerns for decades.

It is not clear exactly how much weapons-grade plutonium or highly enriched uranium has been produced at Yonbyong and where North Korea stores it.

In early 2019, North Korean leader Kim Jong Un offered to dismantle the entire complex if he won extensive sanctions relief during a summit with then-US President Donald Trump.

But the US rejected his offer because it would only be a partial surrender of his nuclear capability.

North Korea is believed to be running multiple other covert uranium enrichment facilities. According to a South Korean estimate in 2018, North Korea might already have manufactured 20-60 nuclear weapons as well.

In recent months, North Korea has warned it would expand its nuclear programme if the United States does not withdraw its “hostile” policy on the North, in an apparent reference to US-led sanctions and regular US-South Korean military drills.

Earlier this month, Kim Jong Un’s powerful sister, Kim Yo Jong, said North Korea would bolster “absolute deterrence” to cope with intensifying US threats.

Lee Jong-joo, from South Korea’s Unification Ministry, has said that South Korea is closely monitoring North Korea’s nuclear and missile activities along with the United States.

But she declined to comment on whether Seoul is seeing signs that the North is reactivating its nuclear facilities.