South Korea's President Yoon Suk Yeol and President Joe Biden announced enhanced nuclear cooperation between the U.S. and South Korea amid North Korean threats.

Ahead of Yoon's arrival, senior U.S. officials told reporters that the two leaders would announce measures to reinforce deterrence against North Korea, including the first deployment of a U.S. nuclear missile submarine to the country in decades.

Washington will deploy imposing military technology, including a ballistic-missile submarine, to South Korea in a show of force, senior U.S. administration officials told reporters in a briefing call. It will be the first such submarine visit since the 1980s, they said.

The officials stressed that no U.S. nuclear weapons would be returned to the peninsula, and South Korea would continue not to have control over the U.S. nuclear arsenal.

South Korea will also reaffirm its commitment to the nuclear non-proliferation treaty and its non-nuclear status, they said.

"This is modeled after what we did with European allies during the height of the Cold War in similar periods of potential external threat," said one senior Biden administration official.

The agreed steps fall short of what some in South Korea have called for and are unlikely to alter the direction of North Korea's own nuclear program. But they could allow Yoon to argue to his domestic audience that Washington is taking South Korea's concerns seriously.

What will be known as the Washington Declaration will also create a U.S.-South Korean consultative group, giving Seoul more information and input on nuclear policy – although Washington will retain sole command of its weapons, officials said.

The arrangement – responding to ever-growing tension over communist North Korea's missile tests and nuclear arsenal – echoes moves last seen when Washington oversaw the defense of Europe against the Soviet Union.

"The United States has not taken these steps, really, since the height of the Cold War with our very closest handful of allies in Europe. And we are seeking to ensure that by undertaking these new procedures, these new steps, that our commitment to extended deterrence is unquestionable," a senior official said.

The officials, speaking on condition of anonymity, stressed that there are no plans to station US nuclear weapons in South Korea -- a difference from the Cold War, when U.S. strategic weapons were deployed to Europe.

In addition, Seoul will reiterate its pledge in the declaration not to seek its own nuclear arsenal.

Submarine, aircraft carriers

"We'll announce that we intend to take steps to make our deterrence more visible through the regular deployment of strategic assets, including a U.S. nuclear ballistic submarine visit to South Korea, which has not happened since the early 1980s," an official said.

In addition to submarines, there will be a "regular cadence" of other major platforms, "including bombers or aircraft carriers," the official said, emphasizing however that there will be "no basing of those assets and certainly not nuclear weapons."

An official said that steps are being taken in advance to defuse potential tensions with Beijing over the tougher military posture.

"We are briefing the Chinese in advance and laying out very clearly our rationale for why we are taking these steps," the official said, adding that the Biden administration is "disappointed that China has been unprepared to use its influence" on North Korea.

Yoon is only the second foreign leader invited for a state visit by Biden. A day filled with high-level meetings and ceremonies will conclude with a lavish state dinner in the historic East Room.

Yoon will address a joint session of Congress on Thursday and have lunch with U.S. Vice President Kamala Harris and Secretary of State Antony Blinken. On Friday, he will visit MIT and Harvard University in Boston, before returning home on Saturday.

A military honor guard and hundreds of guests massed outside the White House where Yoon and his wife, Kim Keon Hee, arrived for a day of pomp and ceremony – and far-reaching geostrategic discussions.

Standing alongside Yoon, Biden lauded what he called the "unbreakable bond" of the countries' "iron-clad alliance," forged in the Korean War seven decades ago.

Biden told Yoon at the start of their Oval Office talks that "we're doubling down on our cooperation as allies even as (North Korea) ramps up its challenges."

Yoon responded by saying that the U.S.-South Korean alliance is not "contractual" but an "everlasting partnership."

On Tuesday, Yoon and Biden visited the Korean War Memorial, which features life-sized steel statues of U.S. soldiers marching during the 1950-53 war against the communist north.

Yoon also laid a wreath at the Tomb of the Unknown Soldier in Arlington National Cemetery and joined Harris for a tour of a NASA facility near Washington.

Yoon, in remarks in the Oval Office with Biden seated by his side, appeared to direct criticism against China and Russia for what the West considers aggressive policies.

"Mr. President, attempts to alter status quo by force, supply chain fragmentation and disruption, challenges in food and energy security are threatening global peace and stability," Yoon said.

North Korea's rapidly advancing weapons programs – including ballistic missiles that can reach U.S. cities – have raised questions about whether the U.S. would really use its nuclear weapons to defend South Korea under what it calls "extended deterrence."

Opinion polls in South Korea show a majority of the public wants Seoul to acquire its own nuclear bombs, a step Washington opposes.

White House national security spokesperson John Kirby told a briefing the summit was expected to produce "major deliverables" on issues like extended deterrence, cyber security, climate mitigation, foreign assistance and economic investment.

Under a new "Washington Declaration," the U.S. will give South Korea detailed insights into, and a voice in, U.S. contingency planning to deter and respond to any nuclear incident in the region through a U.S.-ROK Nuclear Consultative Group, U.S. officials said.

The U.S. is briefing China in advance on the steps, the officials said, a measure nodding to desires to ease the tense relationship in the region.

It is only the second state visit Biden has hosted since he took office two years ago - the first such guest was France's president.

For all the extravagance, Yoon's visit comes at a moment of high anxiety in the region.

A poll released on April 6 by the Asan Institute for Policy Studies in Seoul found 64% of South Koreans supported developing nuclear weapons, with 33% opposed.

Yoon, in an interview with Reuters last week, signaled for the first time a softening in his position on providing weapons to Ukraine, saying his government might not "insist only on humanitarian or financial support" in the event of a large-scale attack on civilians or a "situation the international community cannot condone." The topic is expected to be discussed on Wednesday, along with climate change and cybersecurity.

Washington has looked fondly on Yoon's willingness to help Ukraine and seek rapprochement with Japan, the other key U.S. ally in northeast Asia, and on the wave of Korean tech investment in the U.S. since he took office, which officials say now approaches $100 million.