Seoul, South Korea — North Korea said Friday its new submarine has nuclear attack capabilities after years of development. Leader Kim Jong Un described the milestone as crucial in his efforts to build a nuclear-armed navy to counter the United States and its Asian allies.

The North's official Korean Central News Agency said the vessel, named "Hero Kim Kun Ok," is designed to launch tactical nuclear weapons from underwater but did not specify the number of missiles it could carry and fire.

South Korean officials were skeptical that the submarine would work as North Korea described and said it likely wasn't ready for operational duty. Still, the vessel's development underscored how the North continues to potentially extend the range of its nuclear arsenal with systems that are harder to detect in advance.

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Kim's boasts about the submarine came just days after a senior South Korean official told CBS News that Seoul was concerned North Korea could seek nuclear submarine and satellite technology from Russia in exchange for providing Moscow with badly needed weapons and ammunition for its ongoing war in Ukraine.

Based on Kim Jong Un's comments and photos by North Korean state media, it's likely the submarine is the same one Kim inspected in 2019 while it was under construction. At the time, experts assessed it as an effort to convert an existing Romeo-class submarine.

The submarine appears to have at least 10 launch tubes — four of them apparently larger than the other six — that are possibly designed for missiles.

"This submarine, though heavily modified, is based on 1950s Soviet-origin technology and will have inherent limitations. Nevertheless, in terms of complicating the targeting challenges that the U.S. and its allies will face, the submarine will serve North Korea's purposes," said Ankit Panda, an expert with the Carnegie Endowment for International Peace.

In recent years, North Korea tested a variety of missiles designed to be fired from submarines as it pursued the ability to conduct nuclear strikes from underwater. In theory, such capacity would bolster its deterrent by ensuring a survivable capability to retaliate after absorbing a nuclear attack on land.

Ballistic missile submarines would also add a maritime threat to the North's growing collection of solid-fuel weapons fired from land vehicles that are designed to overwhelm missile defenses in South Korea and Japan.

Still, it would take considerable time, resources and technological improvements for the heavily sanctioned nation to build a fleet of at least several submarines that could travel quietly and execute attacks reliably, analysts say.

Satellite photos analyzed by The Associated Press on Friday placed the submarine and the ceremony that Kim took part in the eastern port city of Sinpo, where North Korea runs a major shipyard developing submarines.

The images, taken just before 8 a.m. local time Thursday by Planet Labs PBC, showed the submarine alongside a dock. The submarine appeared to bear the red-white-and-blue bunting seen in photographs released by North Korean state media on Friday. Other details of the state-released photographs matched known features surrounding the facility.

The submarine still appeared to be at port Friday morning, according to other images taken by Planet. The James Martin Center for Nonproliferation Studies first identified the submarine's location.

In speeches at the vessel's launching ceremony Wednesday and an onboard inspection Thursday, Kim expressed satisfaction that the country has acquired its own nuclear attack submarine to counter the advanced naval assets of the U.S., KCNA said. In July, the U.S. docked a nuclear-capable ballistic missile submarine in South Korea for the first time since the 1980s.

Kim said the country is also pursuing a nuclear-propelled submarine and plans to remodel its existing submarines and surface vessels so they can handle nuclear weapons, describing the building of a nuclear-capable army as an "urgent task."

South Korea's military insisted North Korea was exaggerating the submarine's capabilities. The South's Joint Chiefs of Staff said the North would have needed to increase the size of the bridge and other parts of the original vessel to accommodate missile launch systems, but that the appearance of the new submarine suggested that it could "not be operated normally."

"There are signs of deception or exaggeration," the Joint Chiefs of Staff said in a statement, without elaborating.

Kim in recent weeks has been emphasizing the need to strengthen the country's navy. Some analysts say the focus could be driven by a desire to expand military cooperation with Russia, which has suggested the possibility of combined military exercises between the countries.

Amid speculation that Kim is preparing to visit Russia for a meeting with President Vladimir Putin to discuss North Korean arms sales to replenish Russian reserves drained by its war on Ukraine, Planet Labs imagery of North Korea's Sohae Satellite Launching Station analyzed on Friday showed activity on its new coastal launch pad. A rail-mounted structure at the site, which covers its launch area, had been pulled back to expose the pad beneath, which typically happens ahead of a launch.

North Korea had two failed satellite launches in 2023, but vowed to conduct a third. It wasn't immediately clear if the activity at Sohae, about 75 miles northwest of Pyongyang, was related to the satellite program.

Russia - which has always closely guarded its most important weapons technologies, even from key allies like China - could be unwilling to exchange major technology transfers with North Korea for what's likely to be limited war supplies transported over a small rail link between the countries.

Nuclear-propelled submarines, which can quietly travel long distances and approach enemy shores to deliver strikes, are among a long list of advanced weapons systems Kim has been openly pursuing as he attempts to build a nuclear arsenal that could viably threaten the U.S. mainland. But such vessels are going to be largely unfeasible for the North without external assistance in the near-term, Panda said.

"Russian assistance could be quite helpful here, but it's unclear if Moscow would be willing to share this sensitive technology," he said.

Kim insisted that the submarine revealed this week would be just as daunting to his enemies as the nuclear-propelled submarine North Korea plans to acquire in the future.

"The nuclear attack submarine, for decades a symbol of aggression against our republic, has now become a symbol of our revolutionary power to strike fear into the hearts of our despicable enemies," KCNA quoted Kim as saying.

North Korea previously had only one known submarine capable of firing a missile, but that vessel has a single launch tube and analysts considered it a test platform.

North Korea has an estimated 70-90 diesel-powered submarines in one of the world's largest submarine fleets. But they are mostly aging subs capable of launching only torpedoes and mines, not missiles.

Kim Inae, a spokesperson at South Korea's Unification Ministry, which handles inter-Korean affairs, said during a briefing it was "deplorable" that North Korea was continuing to channel its limited resources into developing weapons while ignoring the struggles of its deeply impoverished people.

She didn't provide a specific answer when asked whether Seoul believes Russia might have provided technological assistance to the North on its new submarine.

KCNA said the launching of the submarine was timed for the  75th anniversary of the country's founding, which falls on Saturday and was to be marked by festivities, including a paramilitary parade.

In:
• Kim Jong Un
• War
• Submarine
• South Korea
• Nuclear Weapons
• North Korea