WASHINGTON — The United States will give South Korea a central role for the first time in strategic planning for the use of nuclear weapons in any conflict with North Korea, in return for an agreement that Seoul will not pursue its own nuclear weapons arsenal, American officials said.
The agreement, which the two sides are calling the Washington Declaration, is a centerpiece of this week’s state visit by President Yoon Suk Yeol of South Korea, who was meeting with President Biden at the White House on Wednesday. The president plans to host Mr. Yoon later in the evening for a state dinner, only the second of his administration.
The visit came at a fraught moment between the two longtime allies after leaked disclosures suggesting the United States had intercepted private conversations within South Korea’s national security council. Classified documents made public in recent weeks recounted conversations among top South Korean officials about American pressure to provide artillery ammunition to Ukraine, despite Seoul’s policy of not arming combatants in active wars.
While South Korea has provided humanitarian aid to Ukraine, it has not supplied weapons directly to Kyiv. Seoul has said it was considering selling 155-millimeter artillery shells to Washington as long as the United States would be the “end user.” According to the leaked documents, a top South Korean official discussed the possibility of selling shells to Poland on the same condition, while understanding they would be passed along to Ukraine anyway.
During brief opening statements in front of journalists in the Oval Office on Wednesday, neither Mr. Biden nor Mr. Yoon addressed the matter or responded to questions in advance of a formal news conference scheduled for the afternoon. But they both lavished praise on each other’s country and hailed the 70-year alliance between the United States and South Korea in effusive terms.
Mr. Biden called the relationship the “linchpin of regional security and prosperity,” adding, “Today I’m proud to say, Mr. President, that I think our partnership is ready to take on any challenges.”
He mentioned their “shared commitment to stand with Ukraine and defend its democracy against Russia’s assault” without saying anything concrete about any further help he would ask from Mr. Yoon.
“Our alliance is an alliance of values based on our shared universal values of freedom and democracy,” Mr. Yoon said in response. “It is not a contractual alliance” but an “everlasting partnership.” In perhaps an allusion to the controversy over surveillance, he added, “Together we can resolve any issues between us.”
The two said little about North Korea in the opening statements beyond a general commitment to resolve in the face of Pyongyang’s nuclear weapons program. “We’re doubling down on our cooperation as allies even as the D.P.R.K. ramps up its challenges,” Mr. Biden said, using the North’s initials without adding anything specific about the nuclear commitments that administration officials previewed.
The new cooperation agreement is closely modeled on how NATO nations plan for possible nuclear conflict, but the American president will retain the sole authority to decide whether to employ a nuclear weapon. While the United States has never formally adopted a “no first use” policy, officials said such a decision would almost certainly come only after the North itself used a nuclear weapon against South Korea.
John F. Kirby, a spokesman for the National Security Council, said, “I would caution anyone from thinking that there was new focus on the centrality of nuclear weapons,” despite the wording of the new declaration. “We have treaty commitments to the Republic on the peninsula,” he said, using the shorthand for the Republic of Korea, and “we want to make sure we have as many options as possible.”
The accord is notable for several reasons. First, it is intended to provide assurance to the South Korean public, where pollsters have found consistent majorities in favor of building an independent South Korean nuclear force. Mr. Yoon himself mused openly about that option early this year, though his government quickly walked the statement back. He also raised the possibility of reintroducing American tactical nuclear weapons to South Korea, a step that his government has said in recent weeks it is no longer pursuing.
The United States withdrew its last nuclear weapons from Korea in 1991, under the George H.W. Bush administration.
But the second reason it is important is one the Biden administration is saying little about: It edges toward reversing the commitment, going back to the Obama administration, to reduce the role of nuclear weapons in American defense strategy. For years, the United States has been improving its non-nuclear strike options, improving the precision and power of conventional weapons that could reach any target in the world in about an hour.
But the South is looking for greater assurance of “extended deterrence,” the concept that the United States will seek to deter a North Korean nuclear strike on the South with a nuclear response — even if that risks a North Korean strike on an American city.
South Korea is a signatory to the Nuclear Nonproliferation Treaty, which prohibits it from obtaining nuclear weapons. So the commitment not to build its own weapons is not new. But nations can withdraw from the treaty, simply by providing notice to the United Nations. Only one nation has done so: North Korea, in 2003. Three countries have not signed the treaty and have developed nuclear weapons: Israel, India and Pakistan.
