Seoul, South Korea — North Korea offered a rare glimpse into a secretive facility to produce weapons-grade uranium as state media reported Friday that leader Kim Jong Un visited the area and called for stronger efforts to “exponentially” increase its number of nuclear weapons.

It’s unclear whether the site is at North Korea’s main Yongbyon nuclear complex, but it’s the North’s first disclosure of a uranium-enrichment facility since it showed one at Yongbyon to visiting American scholars in 2010. While the latest unveiling is likely an attempt to apply more pressure on the U.S. and its allies, the images released by North Korean media of the area could provide outsiders with a valuable source of information for estimating the amount of nuclear ingredients North Korea has produced.

During a visit to the Nuclear Weapons Institute and the facility producing weapons-grade nuclear materials, Kim expressed “great satisfaction repeatedly over the wonderful technical force of the nuclear power field” held by North Korea, the official Korean Central News Agency reported.

KCNA said Kim went around the control room of the uranium enrichment facility and a construction site that would expand its capacity for producing nuclear weapons. North Korean state media photos showed Kim being briefed by scientists while walking along long lines of centrifuges. KCNA didn’t say when Kim visited the facilities or where they are located.

 KCNA said Kim stressed the need to further augment the number of centrifuges to “exponentially increase the nuclear weapons for self-defense,” a goal he has repeatedly stated in recent years. It said Kim ordered officials to push forward the introduction of a new type of centrifuge.

Kim said North Korea needs greater defense and preemptive attack capabilities because “anti-(North Korea) nuclear threats perpetrated by the U.S. imperialists-led vassal forces have become more undisguised and crossed the red line,” KCNA said.

South Korea’s Unification Ministry strongly condemned North Korea’s push to boost its nuclear capability. A ministry statement said North Korea’s “illegal” pursuit of nuclear weapons in defiance of U.N. prohibitions is a serious threat to international peace. It said North Korea must realize it cannot win anything with its nuclear program.

North Korea first showed a uranium enrichment site in Yongbyon to the outside world in November 2010, when it allowed a visiting delegation of Stanford University scholars led by nuclear physicist Siegfried Hecker to tour its centrifuges. North Korean officials then reportedly told Hecker that 2,000 centrifuges were installed and running at Yongbyon.

Satellite images in recent years have indicated North Korea was expanding a uranium enrichment plant at Yongbyon. Nuclear weapons can be built using either highly enriched uranium or plutonium, and North Korea has facilities to produce both at Yongbyon. Some U.S. and South Korean experts believe North Korea is covertly running at least one other uranium-enrichment plant.

It’s not clear exactly how much weapons-grade plutonium and highly enriched uranium have been produced at Yongbyon and elsewhere. In 2018, a top South Korean official told parliament that North Korea was estimated to have already manufactured 20-60 nuclear weapons, but some experts say the North likely has more than 100. Estimates of how many nuclear bombs North Korea can add every year vary, ranging from six to as many as 18.

“For analysts outside the country, the released images will provide a valuable source of information for rectifying our assumptions about how much material North Korea may have amassed to date,” said Ankit Panda, an expert with the Carnegie Endowment for International Peace.

“Overall, we should not assume that North Korea will be as constrained as it once was by fissile material limitations. This is especially true for highly enriched uranium, where North Korea is significantly less constrained in its ability to scale up than it is with plutonium,” Panda said.

In 2018, Hecker and Stanford University scholars estimated North Korea’s highly enriched uranium inventory was 250 to 500 kilograms (550 to 1,100 pounds), sufficient for 25 to 30 nuclear devices.

The North Korean photos released Friday showed about 1,000 centrifuges. When operated year-round, they would be able to produce around 20 to 25 kilograms (44 to 55 pounds) of highly enriched uranium, which would be enough to create a single bomb, according to Yang Uk, a security expert at Seoul’s Asan Institute for Policy Studies.

The new-type centrifuge Kim wants to introduce is likely an advanced carbon fiber-based one that could allow North Korea to produce five to 10 times more highly enriched uranium than its existing ones, said Lee Choon Geun, an honorary research fellow at South Korea’s Science and Technology Policy Institute.

Since 2022, North Korea has sharply ramped up its weapons testing activities to expand and modernize its arsenal of nuclear missiles targeting the U.S. and South Korea. Analysts say North Korea could conduct a nuclear test explosion or long-range missile test ahead of the U.S. presidential election in November with the intent of influencing the outcome and increasing its leverage in future dealings with the Americans.

“Overall, the message they are trying to send is that their nuclear capability is not just an empty threat, but that they are continuing to produce (bomb fuel),” Yang said. “And who are they speaking to? It could obviously be South Korea but also certainly the U.S.”

Kim’s recent nuclear drive comes as North Korea is deepening its military cooperation with Russia. The U.S. and South Korea have accused North Korea of supplying badly needed conventional arms to support Russia’s war in Ukraine in return for military and economic aid.

On Friday, a Russian delegation led by the country’s Security Council secretary, Sergei Shoigu, traveled to North Korea and met Kim for talks on bilateral and international issues, Russian media reported. In July 2023, Shoigu, then defense minister, visited North Korea and met Kim.