The United States should focus on curbing North Korea's nuclear and missile threats and reaffirm nuclear protection of South Korea, including giving Seoul a greater say in its nuclear contingency planning, if it wants to keep the Asian ally away from a nuclear path, a former senior U.S. official said.

Robert Einhorn, who served as a top State Department nonproliferation official, made the point in a lengthy article to the Bulletin of the Atomic Scientists, stressing that recent calls in South Korea for nuclear armament "should not simply be dismissed as the provocative view of a vocal minority."

"Seoul's continued nuclear abstinence cannot be taken for granted," Einhorn said in the article written jointly with Kim Du-yeon, a nuclear policy expert who is currently a visiting senior fellow at the Korean Peninsula Future Forum, a think tank in Seoul.

"To keep the probability of a nuclear-armed ROK low, the United States will have to make curbing North Korea's strategic programs and reassuring its ally about the reliability and effectiveness of its nuclear umbrella key components of U.S. policy in the years ahead," he said.

North Korea's fourth nuclear test in January rekindled calls in South Korea for nuclear armament, with some leading members of the ruling party arguing that it makes no sense to rely on the U.S. "nuclear umbrella" as the North's nuclear arsenal grows.

But the government has rejected the idea as running counter to the principle of a nuclear-free peninsula.

Einhorn and Kim said they reached the assessment after conducting a number of interviews with leading members of South Korean society, such as former and incumbent senior government officials, diplomats, military commanders, lawmakers, media and business leaders.

The main motivations behind pro-nuclear arguments include seeking more credible deterrence amid doubts about the U.S. "nuclear umbrella," correcting asymmetry in the military capabilities between the two Koreas, and pressuring China and the U.S. to put in greater efforts to resolve the North Korean nuclear issue, they said.

The authors said that the recent rise in calls for nuclear weapons comes largely from motivations other than the actual desire to acquire them, and that genuine support for acquiring a nuclear arsenal "remains very limited and confined to a vocal minority."

Still, however, the situation could change, they said.

"The key to maintaining support in South Korea for its non-nuclear status, especially in the face of an unconstrained North Korean threat, is confidence in the reliability of U.S. security assurances," the experts said. "As long as ROK policymakers and public regard the U.S. nuclear umbrella as effective and dependable, incentives will remain low for seeking an independent nuclear deterrent."

Though most South Koreans trust U.S. security commitment for now, they have questions and concerns if it will continue in the future, the experts said, pointing out negative statements the Republican presidential nominee has repeatedly made of U.S. security commitments overseas.

"Two interrelated factors will be the key determinants of whether South Korea will remain on its non-nuclear course. The first is North Korea. If Pyongyang's strategic programs can be reversed or significantly contained, the possibility that Seoul will opt for nuclear weapons will become even more remote," the experts said.

"Therefore, to reduce incentives for America's East Asian allies to pursue nuclear weapons ... the next U.S. administration will need to make North Korea one of its principal national security preoccupations," they said.

The second factor is to maintain South Korea's confidence in U.S. security assurances and extended deterrence through such measures, such as high-level statements of support by American officials, joint exercises to show collective resolve, and tangible indications such as B-52 and B-2 bomber flyovers, they said.

"Reassurance will also require addressing concerns raised by South Korea's strategic community about the sharing of information and the role of the ROK in extended deterrence," they said, adding that Seoul is no longer content to leave the job of nuclear deterrence to the U.S.

The U.S. should find ways of accommodating South Korean interest in making a more substantial contribution to the combined deterrence, while at the same time preserving the U.S. president's nuclear prerogatives and flexibility to adapt to a wide range of contingencies, they said.

"The allies will need to consult closely on such critical deterrence issues as where to deploy, and how and when to re-deploy, U.S. strategic assets, including nuclear-capable aircraft and even nuclear weapons," the experts said.  

"While ultimately such decisions will be made by the United States, it is essential that they fully take into account ROK perspectives on how best to ensure an effective deterrent," they said. (Yonhap)