North Korea has completed external construction of a new facility at its main nuclear research center in Yongbyon, according to the head of the U.N. nuclear watchdog, while continuing to operate its nuclear reactors in support of uranium enrichment.

In a statement to the International Atomic Energy Agency (IAEA) Board of Governors on Monday, Director-General Rafael Grossi said the agency is continuing to monitor development of the new building at Yongbyon with similar dimensions to a uranium enrichment facility at Kangson.

“The new building is externally complete and internal fitting is likely underway,” he reported.

The new site also shares similar infrastructure capabilities to Kangson, including power supply and cooling capacity, according to Grossi.

Despite the similarities, the IAEA chief did not specifically categorize the new site as an enrichment facility.

Grossi previously reported in June that North Korea had begun constructing the building at Yongbyon, without giving details about the facility.

NK News analysis of Planet Labs satellite imagery at the time indicated construction preparations for the facility began in late 2024, after which some other buildings at the site were knocked down in Jan. 2025. The new facility is located around 1.4 miles up a winding road from the main Yongbyon complex, despite there being adequate land close to the older site.

A comparison of satellite images taken in September and January appears to confirm Grossi’s statement that exterior work on the blue-roofed building has mostly finished.

Expressing “serious concern” about the ongoing enrichment activities at Kangson and Yongbyon, Grossi presented other updates related to the latter site’s operations.

Grossi said the IAEA has observed a 5MW(e) reactor at Yongbyon operating in its seventh irradiation cycle, an assessment the agency also reported last year.

Yongbyon’s radiochemical laboratory was observed to be active between Jan. and Sept. 2025, and fuel from the reactor’s sixth cycle was likely reprocessed during that period, he added.

Grossi also said Yongbyon’s light water reactor appears to be back in operation after a shutdown between August and November. He did not indicate possible reasons for the temporary suspension of operations during that period.

The IAEA chief did not present specifics of the ongoing operations at the Kangson uranium enrichment plant, whose existence was confirmed after a visit by Kim Jong Un in Sept. 2024. 

North Korean state media has never named the facility, but NK Pro analysis at the time identified it as a Kangson complex long suspected of being a nuclear plant. Grossi subsequently confirmed Kangson as the site of the enrichment facility.

Kim’s unusually public visits to uranium enrichment sites at Kangson and later Yongbyon underscored his intent to build up North Korea’s nuclear forces and “preemptive strike capability,” which state media framed as a necessary response to the U.S. and its allies having “crossed the red-line.” 

On Monday, Grossi also stated that there are “no indications of significant changes” at North Korea’s main nuclear test-site at Punggye-ri. 

The IAEA added that the site “remains prepared to support a nuclear test,” repeating an assessment he has made on multiple occasions since 2022, when North Korea began restoring a previously demolished tunnel at Punggye-ri.

“The continuation and further development of the DPRK’s nuclear program are clear violations of relevant U.N. Security Council resolutions and are deeply regrettable,” Grossi said. 

“The Agency continues to maintain its enhanced readiness to play its essential role in verifying the DPRK’s nuclear program.”

Colin Zwirko contributed reporting to this article. Edited by Bryan Betts