In the wake of North Korea’s third nuclear test, the security dynamics in the region appears to be entering a new phase as Seoul and Washington push for more potent sanctions and craft ways to beef up their deterrence capabilities.

President Lee Myung-bak and his U.S. counterpart Barack Obama pledged to work out a stronger response and maintain Washington’s nuclear umbrella to protect South Korea during a phone conversation late Tuesday.

They agreed to “seek a range of measures aimed at impeding North Korea’s nuclear and ballistic missile programs and reducing the risk of proliferation,” the White House said in a statement.

“President Obama unequivocally reaffirmed that the United States remains steadfast in its defense commitments to the Republic of Korea, including the extended deterrence offered by the U.S. nuclear umbrella.” 

Lee also spoke over the phone with Japanese Prime Minister Shinzo Abe.

Next week, military officials from the two countries will meet in Washington to discuss their nuclear deterrence strategy, defense sources said Wednesday.

The two allies aim to establish a tailored nuclear deterrence plan by the end of 2013. They are likely to expedite the consultations in line with the North’s elevated nuclear threat.

The U.N. Security Council strongly condemned the detonation during an emergency closed-door meeting Tuesday and vowed action against the “grave violation” of its resolutions.

South Korea and the U.S. are pushing for a fresh round of powerful sanctions despite China’s lukewarm participation. They are calling for measures in line with “significant action” codified in the council’s recent resolution designed to punish Pyongyang for its Dec. 12 rocket launch. Seoul currently holds the presidency of the council this month.

The multilateral mechanism aside, Seoul and Washington are also considering separate, country-level sanctions that are more enforceable and can inflict a bigger blow on its nuclear programs, such as possibly targeting the North’s financial assets or sea transport.

The Unification Ministry said Wednesday it will adjust the level of already feeble inter-Korean cooperation.

“There are various policy tools to change North Korea’s attitude,” spokesperson Kim Hyung-suk said, citing measures targeting inter-Korean exchanges, multinational instruments and those on a country level. “You need to look at those policy tools comprehensively.”

But the Gaeseong Industrial Complex will remain intact, he said, adding that its operation has been already scaled down reflecting the “grave” cross-border tension.

With Pyongyang apparently inching closer to a nuclear weapons state, some experts called for a shift in the focus of disarmament talks to nonproliferation from denuclearization, saying it is the only exit for the long-festering nuclear standoff.

In 2003 the North left the Nuclear Nonproliferation Treaty, an international accord aimed at preventing the spread of nuclear weapons and related technology.

“The world’s focus must now be on containing North Korea and preventing it from proliferating its weapons of mass destruction,” Michael Auslin, an East Asia specialist at the American Enterprise Institute, wrote Tuesday.

“That means acknowledging North Korea is a nuclear state, and one that has a ballistic-missile capability, to boot. The game has moved, then, to limiting the fallout from Pyongyang’s nuclear program, and ensuring that it does not sell or transfer technology or weapons to Iran, other rogue regimes, or even terrorist groups.”

But other officials and experts have expressed skepticism about the change. They also worry that recognizing its atomic-armed status may embolden other rogue states and nuclear aspirants and fuel an arms race in the region and beyond.

While Obama has yet to signal a shift in his “strategic patience” strategy, South Korea’s President-elect Park Geun-hye vowed to balance engagement and deterrence through her signature “trust-building” process policy.

“Nonproliferation may seem to be a doable option to break the current deadlock with North Korea. But it must take substantial risks for political leaders not just to abandon the denuclearization concept but also to talk your own allies and partners into following suit, given saber-rattling and provocations we’ve seen all the while,” a senior Foreign Ministry official said on condition of anonymity due to the sensitivity of the subject.

“It’s like you admit the failure of diplomacy, which the international community has prioritized for so long in resolving any confrontation, and end up acceding to demands of a rogue state. I don’t think either Seoul or Washington is ready for that.”

By Shin Hyon-hee (heeshin@heraldcorp.com)