South Korea’s interest in nuclear weapons hasn’t gone away - it’s just on hold

South Korea is surrounded by nuclear powers and many among the public and in the elite political class are still in favor of the country developing its own nuclear weapons.

President Yoon Suk Yeol signed the pact, but one of the most prominent voices supporting nuclear weapons for South Korea comes from his own ruling partly: Seoul Mayor Oh Se-hoon.

“Only nukes can counter nukes," Oh said in an interview at his City Hall office.

Oh, 62, said the regional security threat has risen so high that it would justify triggering Article X of the Nuclear Nonproliferation Treaty, which South Korea signed nearly five decades ago.

Despite U.S. assurances of protection, South Korea is surrounded by three nuclear-armed nations—China, Russia and North Korea. Those countries could pursue joint naval drills, Seoul’s spy agency has told lawmakers. North Korean leader Kim Jong Un and Russian President Vladimir Putin metin Russia recently, discussing ways to bolster ties and thwart the U.S.-led global order.

Many South Koreans want nukes

The open discourse by South Korea’s political elite crosses the partisan spectrum and has emerged anew in recent years. That, in large part, reflects broad public backing for a nuclear program: a strong majority of South Koreans have supported the notion for a decade.

Oh, a former attorney who began his second stint as mayor in 2021, isn’t alone among leading South Korean politicians calling for South Korean armament. They argue that relying on Washington’s nuclear umbrella isn’t enough.

Conservative lawmakers gathered at a conference earlier this year and discussed the prospect of South Korea’s nuclear development. Tae Yong-ho, a former senior North Korean diplomat who defected and is now a lawmaker in South Korea, said nuclear anxieties haven’t gone away and suggested developing nuclear weapons as a way to reduce the Kim regime’s threat. Ruling party leader Kim Gi-hyeon has consistently said acquiring nuclear weapons is the only way to preserve peace on the Korean Peninsula.

The party’s interest in the topic had risen after Yoon, who took office last year, said in January that South Korea could develop its own nuclear weapons or ask the U.S. to redeploy them, rattling Washington officials. Hedialed backthe remarks a week later.

Three months later, Yoon met President Biden at the White House, promising not to pursue a nuclear bomb. In exchange, Seoul won more frequent visits to the region by U.S. nuclear assets meant to deter Pyongyang, and greater consultation on potential American nuclear use in the event of a Kim regime attack.

Following the leader-to-leader pact called the “Washington Declaration," South Korean support for nuclear armament dropped to 60% this year, about a nine-percentage-point fall from the prior year, according to a recent survey by Korea Institute for National Unification, a state-funded think tank in Seoul. Trust in the U.S. nuclear umbrella, which includes South Korea, rose modestly to 75%.

A majority of both conservatives and liberals back South Korea going nuclear, with widespread acknowledgment that doing so won’t convince North Korea to give up their weapons, according to polling by the Chicago Council on Global Affairs.

“To dismiss this as a fringe movement is a pretty serious mistake," said Karl Friedhoff, one of the report’s authors and a fellow in public opinion and Asia policy at the organization.

Support for nuclear armament in South Korea won’t go away, especially as the nuclear arsenals of Russia, China and North Korea raise concerns about South Korea’s ability to defend itself, said Shin Yul, a professor of political science at South Korea’s Myongji University.

“The recent statements with Washington temporarily put out the fire, but as long as South Koreans fear North Korea’s growing nuclear threat, politicians will continue to call for nuclear armament," Shin said.

South Korea has the technology

Seoul has roughly 10 million people, representing about one-fifth of South Korea’s total population. Oh, as Seoul mayor, is seen as the country’s second most powerful elected official. He is the only local government official given ministerial-level treatment. He can participate in presidential cabinet meetings, meaning he has a direct channel to the president.

Oh said it was time for South Korea to accept that North Korea is a nuclear power. In 1991, following the end of the Cold War, the U.S. removed tactical nuclear weapons it had deployed in South Korea. Despite the “blood alliance" with the U.S., trusting that Washington will protect Seoul under any circumstances isn’t enough, Oh said.

“If the U.S. stationed nuclear weapons here, we wouldn’t have to talk about developing our own nuclear weapons," he said.

Seoul has the technology, funds and nuclear power plants that can be used toward building nuclear weapons, Oh argued. Within a year, South Korea could develop nuclear weapons just like China or Russia, he said.

Nuclear experts echo Oh’s assessment that South Korea has the technology, facilities and funds to produce highly enriched uranium and plutonium needed for nuclear weapons. It would take several months to produce fissile material, and about a year to make one or two nuclear bombs if South Korea were to focus its resources on nuclear development, according to Kang Jung-min, the former chairman of South Korea’s Nuclear Safety and Security Commission.

But this timeline doesn’t factor in potential sanctions on uranium imports or the controversial process of determining where the nuclear-testing facilities would be located, nuclear experts say. In response to a nuclear-pursuant South Korea, the U.S. could terminate defense sales and military assistance as well.

“South Korea has the technology to develop nuclear weapons, but nuclear armament will lead to severe economic sanctions and raises the risk of nuclear war," Kang said.

Write to Dasl Yoon at dasl.yoon@wsj.com and Timothy W. Martin at Timothy.Martin@wsj.com