President Yoon Suk Yeol, right, and his U.S. counterpart Joe Biden shake hands during the North Atlantic Treaty Organization (NATO) summit in Washington D.C., July 11. Yonhap

President Yoon Suk Yeol and U.S. President Joe Biden warned Thursday that any North Korean nuclear attack against South Korea will be met with a "swift, overwhelming and decisive" response, as they highlighted "tremendous" progress in their joint deterrence efforts.

Following their meeting on the margins of a NATO summit in Washington, they issued the warning in a joint statement that commended the signing of the allies' nuclear deterrence guidelines designed to ensure the credibility of America's "extended deterrence" commitment to South Korea in an integrated manner.

"The presidents reaffirmed their commitments in the U.S.-ROK Washington Declaration and highlighted that any nuclear attack by the DPRK against the ROK will be met with a swift, overwhelming and decisive response," the statement read.

ROK and DPRK stand for the official names of South Korea and North Korea, the Republic of Korea and the Democratic People's Republic of Korea, respectively.

Seoul's defense ministry and the Pentagon signed the "Guidelines for Nuclear Deterrence and Nuclear Operations on the Korean Peninsula" in an apparent deterrence message amid growing concerns over North Korea's unceasing pursuit of advanced nuclear and missile programs and its deepening military alignment with Russia.

The guidelines document is a key byproduct of the allies' Nuclear Consultative Group (NCG) launched last July based on the Washington Declaration that Yoon and Biden issued at their White House summit last April to enhance the credibility of the United States' extended deterrence.

Extended deterrence refers to the U.S.' commitment to defend its ally with all of its military capabilities, including nuclear arms.

In their joint statement, the two leaders highlighted the alliance's readiness to face down North Korean threats.

"Biden reiterated that the U.S. commitment to extended deterrence to the ROK is backed by the full range of U.S. capabilities, including nuclear," it said. "Yoon reiterated that the ROK's full range of capabilities will greatly contribute to the alliance's combined defense posture."

The signing comes after Russian President Vladimir Putin and North Korean leader Kim Jong-un signed a "comprehensive strategic partnership" treaty during last month's summit in Pyongyang, which has stoked security concerns over the two countries' tightening military alignment.

Their meeting is seen as part of efforts to reaffirm Washington's security commitment to South Korea as deepening relations between Russia and North Korea are refueling the debate over whether South Korea should have its own nuclear program.

The deterrence guidelines involve South Korea's role to provide conventional military support for U.S. nuclear operations in a contingency.

The NCG sets up the guidelines for joint efforts to enable "joint planning and execution" for South Korea's conventional support for U.S. nuclear operations in a contingency, the statement said.

"The NCG also facilitates continuous improvement to U.S.-ROK combined exercises and training activities, including through regularized table-top exercises and whole-of-government simulations," it noted.

South Korea and the U.S. will conduct Ulchi Freedom Shield, a joint, combined, and interagency exercise held in late August that will reflect some of the guidelines for the first time.

First Deputy National Security Adviser Kim Tae-hyo said the NCG document provides both principles and guidelines for the alliance's nuclear deterrence policy and nuclear operations.

"This is the first time that it has been explicitly stated in a document that U.S. nuclear assets will be assigned to missions for deterring and responding to North Korean nuclear threats," Kim said in a press briefing.

"The U.S.-ROK alliance, which has been based on conventional forces, has now been firmly elevated to a nuclear-based alliance," he added. (Yonhap)