Kim Jong Un’s latest flaunt: A secret nuclear site now shown in public

SEOUL—With his ties with Russia strengthening, North Korean leader Kim Jong Un no longer feels the need to hide one of his top-secret nuclear facilities from the outside world.

Photos run Friday in North Korean state media showed Kim strolling past rows of metal centrifuges—machines that enrich uranium—with officials by his side. He conducted an on-site inspection of the country’s Nuclear Weapons Institute and the uranium-enrichment base. The 40-year-old dictator also demanded an exponential increase in the country’s nuclear arsenal.

The brazenness shows how little Kim fears attracting international blowback over his sanctions-violating nuclear program. In recent months, North Korea has test-fired weapons and showcased new nuclear-capable missile launchers. Pyongyang knows it has Moscow’s veto at the United Nations Security Council to protect it from punishment.

North Korea’s relations with Russia have flourished since Russia’s full-scale invasion of Ukraine, as the two isolated countries aligned over distrust of the U.S.-led world order. Russian soldiers are firing North Korea-supplied missiles in Ukraine, according to assessments from Washington, Seoul and Kyiv. During Russian President Vladimir Putin’s visit to Pyongyang in June, the two countries signed a mutual defense treaty. Putin said at the time he wouldn’t rule out offering military-technical cooperation to Pyongyang.

Underscoring that growing closeness: The photos’ release came on the same day Kim met with Sergei Shoigu, the head of Russia’s Security Council, in Pyongyang.

North Korea first openly acknowledged its uranium-enrichment program in 2009, following many years of denials. But never before had the country published images from inside its facilities, Pyongyang observers say.

North Korea is trying to draw attention to its rapidly advancing nuclear program in an “unusual way” by revealing photos of a very secretive defense facility that most countries would keep hidden, said Hong Min, a senior research fellow at the Korea Institute for National Unification, a South Korean government-funded think tank.

What is more concerning, is that Russia could provide raw materials for the production of new centrifuges or technical support for maintaining North Korea’s uranium enrichment facilities, Hong said. “North Korea claims to be using its own technology, but I suspect Russian help could be involved,” he said.

Russia has expanded security ties with Iran and North Korea since its invasion of Ukraine, and the U.S. adversaries have charged ahead with increasing nuclear materials.

A recent report by the U.N.’s atomic agency said Iran was expanding its stockpile of near-weapons-grade uranium, which could lead to enough enriched uranium to fuel nuclear bombs. Meanwhile, apart from North Korea’s main Yongbyon nuclear complex, another suspected uranium enrichment facility has been expanded this year, the agency’s director general said this week.

South Korean officials have said North Korea began pursuing a uranium-enrichment program in the mid-1990s. That work represented an additional route to building a nuclear bomb from its plutonium program.

The first U.S.-North Korea deal on nuclear disarmament broke down, after Washington discovered the Kim regime’s undisclosed uranium program in the early 2000s.

In 2010, North Korean officials told a visiting U.S. inspector, Siegfried S. Hecker, that the country operated around 2,000 centrifuges. Pyongyang hasn’t offered subsequent specifics on how broadly production capacity has since expanded.

From Friday’s photos, it is difficult to tell which uranium enrichment facility Kim was inspecting. But it is clear that Kim’s intent is to mass produce nuclear materials and increase North Korea’s stockpile of nuclear bombs, said Park Won-gon, a professor of North Korean studies at Ewha Womans University in Seoul.

“Kim is telling the U.S., ‘Accept us as a de facto nuclear state,’” Park said.

Write to Dasl Yoon at dasl.yoon@wsj.com