According to the U.N. Atomic Agency, North Korea seems to have restarted operation of its main nuclear reactor that produces weapons fuels. This comes as North Korea openly threatens to expand its nuclear arsenal in the midst of long-dormant nuclear diplomacy.

The International Atomic Energy Agency’s annual report refers to a 5-megawatt nuclear reactor located at North’s main nuclear facility in Yongbyon (north of Pyongyang). This reactor produces plutonium which is one of the key ingredients in nuclear weapons construction, along with highly enriched and uranium.

According to the Friday IAEA report, “Since the beginning of July 2021 there have been indications, including cooling water being discharged, consistent with the operation and maintenance of the reactor.”

According to the report, there was evidence that Yongbyon’s laboratory for radiochemical research operated from mid-February through early July this year. This period of operation was consistent with the previous North Korean reprocessing campaigns of irradiated-fuel discharged from the reactor. This laboratory extracts plutonium by reprocessing spent fuel rods from reactors.

“North Korea’s nuclear activities remain a serious concern. The IAEA stated that the IAEA found new evidence of operation of the 5-megawatt radiochemical laboratory and of the reactor at 5 megawatts.

Since 2009, when North Korea expelled IAEA inspectors, the IAEA hasn’t had access to Yongbyon and other locations. According to the agency, it uses satellite imagery as well as open source information in order to track developments in North Korea’s nuke program.

The Yongbyon nuclear fuel complex also produces highly enriched uranium. According to the IAEA, there were “indications” that the centrifuge enrichment facility reported was not operational for some time. However, regular vehicular movements were still observed.

This complex, which North Korea refers to as “the heart” its nuclear program, research and development, has been at center of international concern for decades. It is not known how much weapons-grade or highly enriched uranium was produced at Yongbyon, nor where it is stored.

Kim Jong Un, North Korean leader, offered to demolish the entire complex if he received extensive sanctions relief at a summit with Donald Trump in early 2019. The Americans turned down Kim’s offer, as it would be a partial surrender to his nuclear capabilities.

North Korea may have multiple covet uranium enrichment plants. South Korea estimates that North Korea may have already manufactured 20-60 nuclear weapons in 2018.

North Korea has been warning it will expand its nuclear program if the United States does not withdraw its “hostile” policy on North Korea. This apparent reference to U.S. sanctions and U.S. military drills between the two countries isn’t surprising. Kim Yo Jong, Kim’s powerful sister, stated earlier this month that North Korea would increase “absolute defense” in order to withstand intensifying U.S. threats.

Lee Jong-joo was the spokesperson for South Korea’s Unification Ministry. She stated Monday that South Korea closely monitored North Korea’s missile and nuclear activities, as well as those of the United States. She declined to comment on Seoul’s signs of the North activating its nuclear facilities.

Jen Psaki, White House Press Secretary, stated Monday that the Biden Administration was aware of the report. She also said that they were closely coordinating with allies.

She stated that “this report highlights the urgent need to dialogue and diplomacy in order to achieve complete denuclearization on the Korean Peninsula.” “We will continue to seek dialogue (North Korea) in order to address the reported activity as well as all issues related to denuclearization.