SEOUL—North Korea’s nuclear push is triggering a military buildup here and adding fuel to a hot debate over South Korea’s defense strategy—including whether the country should have its own nuclear option.
A few conservative politicians and a small majority in opinion polls have for years supported South Korea getting access to nuclear weapons. Lately, some prominent new voices have joined them, including Kim Jin-pyo, a four-term lawmaker from the main, left-of-center opposition party, who said Seoul needed a “balance of terror” to match North Korea’s threat.
Mr. Kim said nuclear weapons in South Korea would also pressure China and Russia to deal with North Korea more seriously.
Two of South Korea’s major newspapers have recently shifted from caution to strongly supporting the idea of basing U.S. nuclear weapons in South Korea again, 25 years after they were removed in favor of a strategy of “extended deterrence.”
In a report last month, a panel of experts that advises South Korean President Park Geun-hye on policies to reunify the Korean Peninsula also suggested studying the reintroduction of U.S. nuclear weapons.
The U.S. has provided South Korea with military backing since 1953 under a mutual defense treaty. But early this year, U.S. presidential candidate Donald Trump stoked anxieties here with remarks that seemed to call that commitment into question, government officials say.
“At some point we have to say, ‘You know what, we’re better off if Japan protects itself against this maniac in North Korea, we’re better off, frankly, if South Korea is going to start to protect itself,’ ” Mr. Trump told CNN in March.
Such remarks have emboldened some South Korean conservatives who want the country to develop its own arsenal. “As Trump is openly calling for the pullout of U.S. troops from South Korea, the country’s security is like a candle facing a storm,” said Won Yoo-chul, a ruling-party maverick.
The government, however, strongly resists a nuclear option, citing the U.S. umbrella and the negative diplomatic and economic repercussions of opting out of the international nonproliferation regimen. Asked about the experts’ report, the president’s spokesman said: “Our government’s position remains unchanged and we are committed to a nuclear-free Korean peninsula.”
Under a separate bilateral treaty renewed last year, South Korea is barred from creating nuclear material for weapons in return for U.S. fuel for its atomic-power reactors.
American officials say there has been no discussion about redeploying nuclear weapons here. One senior South Korean government official said privately that calls for Seoul to deploy them were “bullshit.”
But as North Korea advances toward a more-threatening arsenal, including nuclear-tipped missiles that could be fired from submarines, discussion in the South over how to respond has intensified. Talk from military officials of pre-emptive strikes if a nuclear attack appears imminent has become frequent.
Uncertainty over Pyongyang’s progress has amplified fears.
“The South Koreans are so nervous because they don’t know what they’re looking at,” said Robert Kelly, a professor of political science at Pusan National University in South Korea.
While Washington and its allies try to find ways to slow Pyongyang’s progress, including through tighter sanctions and diplomatic pressure, Seoul has launched conventional weapons upgrades.
Since April, the government has announced more than a dozen plans for introducing new air, land and sea military technology—an unusually rapid pace. Its defense budget is up 3.6% from actual spending last year, with the biggest increase in funds for new hardware.
Late last month, it said it would spend nearly $400 million on new sonar for ships to track North Korean submarines. Also in the pipeline: fighter aircraft with advanced radar, attack submarines and amphibious assault vehicles.
Seoul also plans to research a laser weapon to target North Korean drones.
“South Korea has one of the most aggressive military modernization programs you’ll see in the region,” said Paul Burton, a defense industry analyst for IHS Jane’s based in Singapore.
South Korean and U.S. officials say shows of force are essential to warn North Korea away from military provocation.
Shortly after North Korea’s Sept. 9 nuclear test, its second this year, American bombers made their closest-ever runs to North Korea’s border, followed by U.S.-South Korean naval drills unusually near the inter-Korean sea divide. The U.S. also landed a B-1 supersonic bomber in South Korea for the first time.
“Our resolve is unwavering, our commitment is ironclad, and we are by your side,” U.S. Ambassador to the United Nations Samantha Power said Sunday in Seoul after visiting U.S. troops at the inter-Korean border.
Immediately after the Sept 9 test, South Korea revealed its plans for destroying its rival’s military command with missiles and special forces in the event of war. Such public statements on the topic are rare.
The defense minister said in parliament that the plan includes targeting North Korean dictator Kim Jong Un—a move that several experts called risky.
“It’s an emotional response that primes North Korea to think it has to attack first,” said Van Jackson, an associate professor at the Asia-Pacific Center for Security Studies in Honolulu and former Pentagon strategist.
Against the rising hawkish voices, some South Korean politicians question the effectiveness of nuclear weapons or shows of force in deterring Mr. Kim.
Joo Seung-young, a member of a minor opposition party, said this month that U.S. bomber flights “might just heighten nuclear tension” on the Korean Peninsula.
Mr. Jackson advocated a de-emphasis of nuclear weapons and more-regular exercises that demonstrate a swift and strong conventional response to the type of limited attacks North Korea has staged in the past, such as the 2010 shelling of a South Korean island.
“What we are doing now is not credible,” he said.
—Min Sun Lee contributed to this article.
Write to Alastair Gale at email@example.com