Yoon announced the agreement during a joint press conference on Wednesday following summit talks with Biden at the White House, outlining a joint statement, dubbed the "Washington Declaration", that they adopted to strengthen "extended deterrence" against the North's nuclear and missile threats, reports Yonhap News Agency.
[bsa_pro_ad_space id=1]Extended deterrence refers to the US commitment to mobilizing all of its military capabilities, including nuclear, to defend South Korea.
"South Korea and the US agreed to immediately hold talks between their leaders in the event of North Korea's nuclear attack, and through them, promised to take swift, overwhelming and decisive action using all of the alliance's military capabilities, including US nuclear weapons," Yoon said at the White House Rose Garden.
He said the two countries agreed to establish a Nuclear Consultative Group (NCG) in order to operate the new extended deterrence system in more detail.
The allies will share information on nuclear and strategic operations and planning and hold regular discussions on how to plan and execute joint operations combining South Korea's cutting-edge conventional capabilities with the US nuclear capabilities, he said.
A presidential official later told reporters in Washington the NCG will be led by deputy minister-level officials from the two countries.
In South Korea, a deputy minister ranks third, after the minister and vice minister.
The group will meet every quarter, four times a year, and report the results of their meetings to their respective presidents.
The two countries will further develop table-top simulation exercises to prepare against a nuclear crisis and regularly and continuously deploy US strategic assets to the Korean Peninsula, Yoon said, while the declaration said an American nuclear ballistic missile submarine will soon visit South Korea.
The leaders also agreed to continue cooperation to further strengthen extended deterrence.
At the press conference, Biden issued a stern warning to the North.
[bsa_pro_ad_space id=1]"A nuclear attack by North Korea against the US, its allies or partners is unacceptable and will result in the end of whatever regime were to take such an action," he said.
The Washington Declaration follows months of work between the allies amid questions about the credibility of the US extended deterrence commitment to South Korea and calls for the country's own nuclear armament as North Korea advances its nuclear and missile capabilities.
As a party to the Nuclear Non-proliferation Treaty, South Korea is banned from developing its own nuclear weapons, while the US maintains a longstanding policy of upholding the non-proliferation regime.
Yoon is on a six-day state visit to the US as the two countries mark the 70th anniversary of the bilateral alliance that emerged from the 1950-53 Korean War. A joint statement following the summit showed the two leaders covered a wide range of topics, including Russia's war in Ukraine, their commitment to diplomacy with North Korea, their deep concern over climate change, and their commitment to maintaining a free and open Indo-Pacific.