President Yoon Suk Yeol and US President Joe Biden hold a bilateral meeting at the White House Oval Office in Washington on Wednesday. (Yonhap)

WASHINGTON -- Presidents Yoon Suk Yeol and Joe Biden warned Kim Jong-un that a nuclear attack by North Korea against the US and South Korea will be responded to with a nuclear counterattack and that will result in the end of the reclusive regime.

“A nuclear attack by North Korea against the United States or its allies or partisans -- partners -- is unacceptable and will result in the end of whatever regime were to take such an action," said Biden at a press conference held after his summit with Yoon.

Yoon also said the US would deploy its strategic assets to the Korean Peninsula “constantly and routinely."

“South Korea and the US have agreed to hold immediate bilateral presidential consultations in the event of North Korea's nuclear attack and respond swiftly, overwhelmingly and decisively by using the full force of the alliance, including the United States' nuclear weapons,” Yoon said.

The remarks came as the allies reaffirmed their 70 years of an "ironclad" alliance by adopting the Washington Declaration, which has, for the first time, documented enhanced extended deterrence against Pyongyang's escalating provocations. They agreed to deploy other strategic assets including US nuclear missile-carrying submarines, which visited South Korea's ports frequently in the late 1970s in the midst of the Cold War.

The declaration also specifies the launch of the Korea-US Nuclear Consultative Group, a nuclear consultation group that guarantees South Korea's participation in the process of providing extended deterrence by the US in case of emergency, such as the threat of North Korean nuclear missiles. South Korea is the first foreign nation to create such a consultative mechanism with the US. The group is expected to offer Seoul additional insight into how the US makes strategic decisions when preparing for contingencies.

“Our two countries will share information on nuclear and strategic weapon operations plans in response to North Korea’s provocations and have regular consultations on ways to plan and execute joint operations that combine Korea’s state-of-the-art conventional forces with the US’s nuclear capabilities, the results of which will be reported to the leaders of our two countries on a regular basis,” President Yoon told the press.

“Korea and the US, based on the Washington Declaration, our two countries have agreed to strengthen extended deterrence, and the implementation level is different from the past,” he said.

The newly established nuclear consultation group is anticipated to play a similar role to the NATO Nuclear Planning Group formed in 1966 following World War II. During that era, the NPG was created proactively to address the Soviet Union's nuclear threat and to relieve the anxiety of European countries.

Unlike some Western European countries where US tactical nuclear weapons have been deployed, the US does not deploy tactical nuclear weapons to the Korean Peninsula. Biden also mentioned when discussing the submarines during the press briefing, that the US is not going to be stationing nuclear weapons on the peninsula.

He emphasized the enduring commitment of South Korea to refrain from pursuing nuclear weapons, though the majority of Koreans express support for nuclear development in reaction to the North Korean provocations.

“And we made it really very, very clear,” Yoon said, adding South Korea has “repeatedly confirmed” its commitment to the nonproliferation treaty.

In a poll released by Gallup Korea in January, 76.6 percent of respondents said they support South Korea's independent nuclear development. It is 17 percentage points higher than the 60 percent of respondents who were in favor of possessing nuclear weapons in a poll released by the same agency in 2017.

On NCG, Kim Tae-hyo, the first deputy director of the National Security Office, told reporters that South Korean and US security officials will meet regularly to discuss nuclear and strategic weapons operations. A senior presidential official said that the NCG will have vice-ministerial level representation. The meeting cycle will be four times a year, and the group is planned to meet two to three times within this year.

On economic cooperation, Biden said the US CHIPS and Science Act, signed into law in August to reduce America’s reliance on foreign-made semiconductors by increasing domestic production, is a win-win for both the US and South Korea.

It is in America’s “overwhelming interests” to see Korean companies succeed and Korea’s economy grow, the US president added, without elaborating how the subsidy plan has led to job growth there. “We’d like to see them grow and I mean that sincerely,” he said.

President Yoon said he welcomed the two countries' cooperation on chips, electric vehicles and batteries, noting “President Biden has said no special support and considerations will be spared for Korean companies’ investment and business activities.”

The two leaders agreed to work together closely on supply chain constraints and advance technology, according to Yoon. During the conference, he did not refer to any loosening of the subsidy rules, something many Korean business leaders had hoped to see happen during Yoon’s state visit.

Companies receiving such federal subsidies under the law have to share part of their profits, one of many requirements US allies -- including South Korea -- argue needs some kind of easing because they are discriminatory.

Yoon's state visit, the first South Korean to do so in 12 years, marks the 70th year of the alliance, which was forged when the 1950-53 the Korean War hostilities were ceasing. The alliance has helped South Korea grow its own defense for decades from consistent threats from North Korea. South Korea has about 28,500 US troops stationed across the country.

After the summit, Yoon and first lady Kim Keon Hee attended a state dinner hosted by Biden and first lady Jill Biden, again reaffirming their alliance.

"The respected sacrifices and actions of those who have supported the Korea-US alliance for the past 70 years have come together, making our alliance a strong alliance to act together toward the future," Yoon said in a speech.

He also likened the alliance as a four-leaf clover, saying "the friendship is like a four-leaf clover: hard to find but lucky once you have it."

"I hope today will be remembered as a historic day on which a four-leaf clover known as the South Korea-US alliance extended new roots beyond the glory of the past 70 years," he said. He then offered a toast, saying, "To our ironclad alliance."

Staff reporters Ji Da-gyum and Choi Si-young contributed to this article in Seoul. -- Ed.