South Korea and the United States should modernize around 100 US tactical nuclear weapons to support the security of the South against North Korea's growing threats, a research report said Monday.

The Asan Institute for Policy Studies and the Rand Corp. made the suggestion in a joint report, stressing the North has "already established a nuclear weapon force that could pose an existential threat" to South Korea and is "on the verge" of posing a serious threat to the US.

"Kim Jong-un appears to be planning a force of at least 300 to 500 nuclear weapons... the 300-weapon threshold could almost be reached in 2030," the report, titled "Options for Strengthening ROK Nuclear Assurance," said.

The report estimated a potential North Korean nuclear attack as powerful as its sixth nuclear test, if launched against Seoul, would lead to nearly 2 million fatalities and serious injuries.

The report also said the North hopes to use its nuclear weapon to threaten Washington in order to break the South Korea-US alliance and "dominate South Korea without having to invade it."

It then called for approximately 100 US tactical nuclear weapons to be modernized at South Korea's expense, saying the weapons could be stored in the US but would be rapidly deployable to and committed to supporting the South.

According to the report, the four-step sequential process to commit US nuclear weapons to the South and pressure the North to freeze its nuclear weapons program will also involve building new US tactical nuclear weapon storage in South Korea and dedicating "all or part of the nuclear weapons on a US ballistic missile submarine operating in the Pacific to targeting North Korea."

The report stressed "if implemented roughly as described, this option could commit up to about 180 US nuclear weapons to ROK security in the next few years" while "perhaps eight to 12 B61 nuclear bombs could be deployed in the ROK for both symbolic and operational purposes." ROK stands for South Korea's official name, the Republic of Korea.

It also pointed out South Korea's assurance in the US nuclear umbrella has faltered due to ambiguity in the US commitment to the South amid increasing North Korean threats, leading to increased calls for Seoul to develop its own nuclear weapons.

The Washington Declaration, in which South Korean President Yoon Suk Yeol and US President Joe Biden agreed to bolster extended deterrence in their April summit, "promises greater strategic clarity," but still "lacks the implementation details that are needed to truly increase ROK nuclear assurance," the report said.

"When dealing with the nuclear weapon threats of North Korea and China, the importance of strategic clarity will only increase in the future." (Yonhap)