President Yoon Suk Yeol on Sunday said South Korea is open to trilateral strategic and nuclear planning with the United States and Japan on how to respond in the event of a North Korea’s nuclear attack.

Yoon underscored that “security cooperation is more important than ever” as South Korea and Japan face common threats from North Korea, during a televised news conference following his in-person summit with Japanese Prime Minister Fumio Kishida in Seoul.

Yoon said he is open to Japan’s engagement in the Washington Declaration, which was signed during the April 26 summit with US President Joe Biden, with the goal to improve the shared decision making process on how to use allied forces.

“The Washington Declaration is a bilateral agreement between Korea and the US, but we do not rule out Japan’s participation,” Yoon told reporters.

“But the Washington Declaration has not been finalized and we must continue discussion to fill in the details of joint planning and execution. Once the discussion gets on track and Japan is ready to cooperate with the US on this matter, we can cooperate (with Japan) at any time.”

The essence of the Washington Declaration is the establishment of the vice-ministerial level Nuclear Consultative Group, which is solely tailored to share information, consultation, joint planning on how to operate US nuclear assets in case of contingencies on the Korean Peninsula.

Kishida also underscored that he and Yoon agreed that the two countries should enhance security cooperation in light of the intricate regional and international security situations.

“We concurred on the importance of enhancing deterrence and response capabilities through Japan-US alliance, South Korea-US alliance as well as security cooperation between Japan and South Korea and among Japan, South Korea, the US in the face of ongoing provocations by North Korea and attempts to unilaterally change the status quo through force in this region,” Kishida said.

Kishida’s rare visit to Seoul would give momentum for the Biden administration's efforts to address economic and security challenges including North Korean threats and China’s growing influence in the Indo-Pacific region through the trilateral context.

The Biden administration underscored that close trilateral cooperation was indispensable to address nearly every major challenge in the region in its Indo-Pacific strategy unveiled in February 2022.

The Yoon-Kishida meeting was also held two weeks before a trilateral meeting which will be held on the sidelines of the G-7 summit in Hiroshima, Japan, from May 19-21. The group has served as a platform to counterbalance China and Russia. Eight other countries including South Korea, Australia, Brazil, India have been invited to the event.

Speaking at the news conference, Yoon said he and Kishida agreed to continue trilateral security cooperation to share North Korean missile warning data in real time. Both also welcomed the progress that the three countries have made since the leaders of the three countries initially made an agreement at the summit in November 2022 to that end.

In particular, South Korea, the United States and Japan have stepped up their trilateral military and security cooperation and sought to improve interoperability of forces in the face of escalating missile and nuclear threats posed by North Korea.

The three countries agreed to regularize ballistic missile defense exercises and anti-submarine warfare exercises to better deter and respond to missile and nuclear threats from North Korea at the high-level Defense Trilateral Talks held this April in Washington.

Seoul, Washington and Tokyo also committed to resuming trilateral exercises, including maritime interdiction and anti-piracy exercises, for the purpose of maintaining peace and stability in the Indo-Pacific region in a more effective manner.