North Korea is displaying a "very serious increase" in its ability to produce nuclear weapons, the head of the United Nations nuclear watchdog warned on Wednesday during a visit to Seoul, the capital of South Korea. Rafael Grossi, Director General of the International Atomic Energy Agency (IAEA), said the agency had confirmed a rapid acceleration in operations at key facilities, raising significant alarm about the scale and pace of the North's weapons programme.

Grossi pointed specifically to heightened activity at the Yongbyon nuclear complex — North Korea's primary nuclear research site — including its reprocessing unit, light-water reactor, and other facilities. The IAEA has also observed the construction of a new building believed to be a uranium enrichment plant, with satellite imagery analysed by the Washington-based Centre for Strategic and International Studies showing generators, fuel storage tanks and cooling units consistent with such a facility. Uranium enrichment provides an alternative — and experts say potentially more efficient — path to weapons-grade material alongside the reprocessing of spent plutonium. Grossi acknowledged the difficulty of making precise assessments without direct access to the sites, but said external analysis pointed to a significant expansion in enrichment capacity. North Korea's total arsenal is currently estimated at a few dozen warheads.

North Korea, a heavily isolated state occupying the northern half of the Korean Peninsula, conducted its first nuclear test in 2006 and has since faced sweeping UN sanctions over its banned weapons programmes. It expelled IAEA inspectors in 2009 and has repeatedly declared it will never relinquish its nuclear arsenal. Asked whether Russia was assisting Pyongyang's nuclear development — amid reports that North Korea has supplied troops and artillery shells to support Russia's war in Ukraine, likely in exchange for military technology — Grossi said the IAEA had not observed evidence of such cooperation, though he cautioned it was too early to draw firm conclusions.

Grossi met South Korean Foreign Minister Cho Hyun, who said Seoul remained committed to reducing hostility with the North and pursuing peaceful coexistence on the peninsula. Separately, senior naval commanders from South Korea, the United States and Japan convened in Seoul on the same day for maritime security talks aimed at countering the North's growing nuclear and missile threats — a sign of deepening trilateral security coordination in the region.

The IAEA's findings underscore the growing challenge facing international nonproliferation efforts. With no inspectors on the ground and diplomatic channels largely frozen, the agency is reliant on satellite imagery and indirect indicators — a significant constraint as North Korea appears to accelerate, rather than slow, its weapons development at a moment of broader geopolitical turbulence.