The United States should take "concrete and meaningful" steps to demonstrate its commitment to South Korea's security in the face of growing nuclear threats from North Korea if Washington wants to keep Seoul from going nuclear, a U.S. expert said.

Ian Williams, a research associate in the CSIS International Security Program, made the argument in an article in the program's monthly newsletter, noting growing calls in South Korea for nuclear armament in the wake of the North's Jan. 6 nuclear test.

"South Korea has serious security threats, and its continued commitment to nonproliferation in the face of those threats should be acknowledged," he said. "It is therefore important that the United States continue to take meaningful and concrete actions to demonstrate its commitment to South Korean security."

Williams said that South Korean President Park Geun-hye has rejected the idea of nuclear armament due mainly to concerns about complicating its relations with the U.S. and China, and risking international sanctions but stressed that "a future ROK president could easily see things differently."

"The Nuclear Non-Proliferation Treaty, to which South Korea is a party, allows a government to withdraw if it 'decides that extraordinary events ... have jeopardized the supreme interests of its country.' Many South Koreans already see their country in a unique security situation," the expert said.

Following the North's nuclear test, some members of South Korea's ruling party raised calls for the deployment of nuclear weapons. On Sunday, Chung Mong-joon, a former ruling party leader, also made a strong case for nuclear armament.

"A lesson from the Cold War is this irony that peace can be maintained when nuclear weapons are responded with nuclear weapons," Chung said in an article posted on his blog.

"Negotiations aimed at ending nuclear weapons can be possible only when we have powerful means corresponding to nukes."

Williams also noted a 2013 opinion poll that showed 66.5 percent of South Koreans said they "supported" or "strongly supported" acquiring nuclear weapons, up from 56 percent in 2010. A 2012 survey also found that only 48 percent of South Koreans have faith in the U.S. nuclear umbrella, down 7 percent from 2011, he said.

"With the international community's apparent inability to roll back North Korea's nuclear development, these trends seem likely to continue," he said.

The expert said that it won't be difficult for South Korea to develop nuclear weapons as the country has a robust nuclear industry in which nuclear reactors produce large quantities of spent fuel that could be reprocessed into plutonium.

"Although it currently lacks reprocessing infrastructure, developing this capability is well within reach of South Korea with its ample resources and deep bench of nuclear expertise," he said.

Should South Korea eventually choose to build a nuclear arsenal, it would do so in a way that fits its geographic and strategic situation, and one possibility would be "small, lower yield nuclear weapons, aimed at eliminating DPRK nuclear forces in a crisis," he said.

In order to buttress eroding confidence in U.S. assurances, Washington should continue working closely with South Korea to "ensure both nations have robust conventional strike capabilities and adequate intelligence to quickly cripple Pyongyang's ability to employ its nuclear weapons, should the need arise," the expert said.

"Reaffirming U.S. extended deterrents in these ways could go a long way to ease South Korea's serious security concerns, and help it maintain its nuclear abstention," he said. (Yonhap)