South Korea is "open-minded" about expanding the existing bilateral nuclear consultative group with the United States to a trilateral framework including Japan, a former South Korean national security advisor said Monday.

Kim Sung-han, President Yoon Suk Yeol's former top national security advisor from 2022 to 2023, acknowledged that during his tenure, he had the opportunity to discuss the idea of the expansion of the framework with his Japanese counterpart.

The Nuclear Consultative Group is a bilateral body created in accordance with the Washington Declaration signed by President Yoon and US President Joe Biden on April 26, 2023. The NCG is tailored to enhance the viability of US extended deterrence and formulate joint response strategies and procedures for the allies in the event of a North Korean nuclear attack on the Korean Peninsula.

Kim underscored that Japan has the final say on the country's participation in the NCG, during an event co-hosted by the Center for Strategic and International Studies and the Korea Foundation in Washington on Monday.

"This is a somewhat sensitive issue to Japan because the NCG is about how to use nuclear weapons in a contingency. So, from the Japanese perspective, this might provoke some domestic discussions," Kim said. "It depends on Japan. Korea is open-minded."

Kim suggested that South Korea and the US have the option to maintain their existing NCG and create a new trilateral NCG involving Japan separately. Alternatively, Japan could gradually join the current South Korea-US NCG.

Kim, however, once again emphasized that this decision ultimately depends on Japan's willingness, which necessitates closer cooperation or consultation beforehand.

In response to Kim's remarks, South Korea's Foreign Ministry said on Tuesday that the government is open to the idea of expanding discussions with Japan, specifically aimed at enhancing cooperation to strengthen extended deterrence.

Extended deterrence is the US commitment to deter or respond to coercion and attacks on US allies and partners by mobilizing the full range of US defense capabilities, including nuclear weapons.

But a senior official at the Foreign Ministry, speaking on condition of anonymity to reporters, explained that the NCG was launched not long ago, in July, with only two meetings convened in July and December of last year.

"Therefore, our current focus lies on institutionalizing cooperation between Korea and the US on extended deterrence," the official said.

"However, the government is fundamentally open to the possibility of whether such consultation between Korea and the US on extended deterrence could evolve into trilateral consultation among Korea, the US, and Japan regarding extended deterrence."

The event also addressed the sustainability of trilateral cooperation despite upcoming legislative elections in April in South Korea, the leadership election of Japan's ruling Liberal Democratic Party in September and the US presidential election in November.

Sung Kim, former US special representative for North Korea, emphasized the "need to institutionalize" trilateral cooperation, extending beyond the military domain to ensure its sustainability regardless of potential shifts in domestic politics.

"Whether it's military exercises, information sharing or cooperation in cyber, once we institutionalize and really establish friendly, cooperative activities among the three countries, it is less likely that they will be affected by elections here, in Tokyo, and in the ROK," Kim said.

The ROK stands for the Republic of Korea, South Korea's official name.

"I believe there is strong interest among the three governments to do exactly that, to ensure that we will, in fact, be able to continue with these activities, irrespective of what happens in elections."

Kim pointed out that events in the US and its decisions on global leadership would influence trilateral cooperation.

But Kim concurrently elucidated the reality is that Japan and South Korea's stature, power and influence have continued to grow regardless of Washington's perspective on trilateral cooperation.

"So, in that sense, it's only natural that there will be greater challenge sharing, burden sharing, among the three countries because we're dealing with two very powerful countries: Japan and the ROK," Kim said.

"I would say, irrespective of what happens in November here, we should expect to see more and more of an active role played by both Japan and the ROK in the global scene."

Kim Sung-han also noted that the "policy environment has been totally changed" when comparing the present to the era of the Trump administration from 2017 to 2021.

Kim explained that the shift in policy dynamics poses a challenge to modifying the current trajectory of reinforcing trilateral cooperation, even in the event of a US presidential candidate favoring isolationist policies or downplaying the significance of alliances.

Kim noted that North Korea has significantly advanced its nuclear and missile capabilities, and new variables such as North Korea-Russia cooperation have emerged. Additionally, efforts to strengthen trilateral cooperation among South Korea, the US and Japan have been prominent.

"If the three of us can make a very much cool-headed assessment of the policy environment, I think we are likely to reach some sort of consensus that could guarantee sustainability," Kim said.