North Korea is making “very serious” advances in its nuclear weapons capabilities, with signs of a new uranium enrichment facility and increased activity at a key complex, the International Atomic Energy Agency chief Rafael Grossi has said.

“Very serious” advances include the likely addition of a new uranium enrichment facility, with heightened activity observed at a key nuclear site.

There has been a rapid rise in activity at the five-megawatt reactor, the reprocessing unit, a light water reactor and other facilities at North Korea’s Yongbyon nuclear complex, Grossi said at a news conference in Seoul, South Korea. The operation of a light water reactor was a key sign that capacity is growing, he added.

"All of them point to a very serious increase in the capabilities of the [Democratic People's Republic of Korea] in the area of nuclear weapons production," Grossi said. 

Grossi also confirmed that the agency had not seen any evidence of Russian technology being used in North Korea’s nuclear weapons programme.

North Korea’s stockpile of nuclear warheads has been estimated at a few dozen.

North Korea has carried out six nuclear weapon tests, according to external reports, intelligence and state media:

• October 2006

• May 2009

• February 2013

• January 2016 (claimed hydrogen bomb).

• September 2016

• September 2017 (claimed thermonuclear weapon)

In May 2012, North Korea changed its constitution to describe the country as a “nuclear-armed state,” according to a U.S. Congress publication in September 2025. It added that North Korea legislated to “take practical steps to bolster up the nuclear deterrence and nuclear retaliatory strike power both in quality and quantity.”

New activity spotted

The watchdog has observed construction of a new facility similar to Yongbyon’s uranium enrichment halls, Grossi said, adding that analysis of external features showed a significant expansion of enrichment capacity.

Addressing agency governors earlier in April, he said the watchdog was monitoring a new building at Yongbyon with similarities to an enrichment facility at Kangson, another key nuclear site near the capital, Pyongyang.

Satellite imagery from April supported the IAEA’s assessment, the U.S.-based Center for Strategic and International Studies said on Monday.

It indicated completion of a suspected uranium enrichment plant capable of producing weapons-grade material, the centre said in a report.

Nuclear weapons as a deterrent

"Moving towards nuclear weapons would never give any country increased security," Grossi said, warning it could instead trigger proliferation.

References in a cooperation pact signed by North Korea and Russia last year appeared to be limited to civilian nuclear projects, though it was too early to draw firm conclusions, he added.

He urged South Korea to work closely with the IAEA to monitor activity and stop proliferation. 

"It is essential that this activity is not conducive to proliferation of nuclear weapons," Grossi said, adding that the IAEA would seek an "ironclad guarantee" against any diversion of the material.

Naval reactors pose particular challenges, as nuclear fuel on submarines can go uninspected for long periods during missions.

South Korea’s submarine ambitions advanced after President Lee Jae Myung and U.S. President Donald Trump finalised joint steps on trade and security last November, in which Washington approved its ally’s plan to build nuclear-powered vessels.

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