SEOUL, South Korea — Keeping diplomatic developments coming at a head-snapping pace, the South Korean government said on Sunday that North Korea’s leader, Kim Jong-un, had told President Moon Jae-in that he would abandon his nuclear weapons if the United States agreed to formally end the Korean War and promise not to invade his country.
In a confidence-building gesture ahead of a proposed summit meeting with President Trump, a suddenly loquacious and conciliatory Mr. Kim also said he would invite experts and journalists from South Korea and the United States to watch the shutdown next month of his country’s only known underground nuclear test site.
In Washington, Trump officials spoke cautiously about the chances of reaching a deal and laid out a plan for the rapid dismantling of the North’s nuclear program, perhaps over a two-year period.
That would be accompanied by a “full, complete, total disclosure of everything related to their nuclear program with a full international verification,” said John R. Bolton, Mr. Trump’s new national security adviser.
The apparent concessions from the youthful leader were widely welcomed as perhaps the most promising signs yet of ending a standoff on the Korean Peninsula frozen in place since fighting in the Korean War ended 65 years ago.
But skeptics warned that North Korea previously made similar pledges of denuclearization on numerous occasions, with little or no intention of abiding by them. Mr. Kim’s friendly gestures, they said, could turn out to be nothing more than empty promises aimed at lifting sanctions on his isolated country.
A South Korean government spokesman, Yoon Young-chan, provided remarkable details of a summit meeting the two Korean heads of state held on Friday, when Mr. Kim made history by becoming the first North Korean leader to set foot in the South.
“I know the Americans are inherently disposed against us, but when they talk with us, they will see that I am not the kind of person who would shoot nuclear weapons to the south, over the Pacific or at the United States,” Mr. Kim told Mr. Moon, according to Mr. Yoon’s account.
It was another in a series of startling statements by Mr. Kim, whose country threatened to do exactly those things during the height of nuclear tensions last year.
Mr. Kim’s apparent willingness to negotiate away his nuclear arsenal was revealed just as Secretary of State Mike Pompeo spoke for the first time about a “good conversation” he had with Mr. Kim during his secret visit to Pyongyang, the North Korean capital, over Easter weekend.
Mr. Pompeo told ABC News in a broadcast on Sunday that the Trump administration’s objective was “complete, verifiable, irreversible denuclearization” with North Korea, and that Mr. Kim was prepared to “lay out a map that would help us achieve” denuclearization.
“We had an extensive conversation on the hardest issues that face our two countries,” Mr. Pompeo said. “I had a clear mission statement from President Trump. When I left, Kim Jong-un understood the mission exactly as I described it today.”
But Mr. Bolton, a longtime critic of past diplomacy with North Korea, expressed skepticism on Sunday, recalling past moments that looked hopeful. Those would include a commitment by Pyongyang in the 1990s to give up its nuclear program and the destruction of a nuclear power cooling tower in 2008 as part of a similar promise.
“We want to see real commitment,” he said on “Face the Nation” on CBS. “We don’t want to see propaganda from North Korea. We’ve seen words. We’ve seen words so far.”
Asked about North Korea’s insistence on a promise by the United States not to invade, Mr. Bolton noted that was an old demand that had been rolled out on other occasions. “We’ve heard this before,” he said. “The North Korean propaganda playbook is an infinitely rich resource.”
Mr. Trump sees the potential for a historic deal with Mr. Kim, “a breakthrough nobody would have imagined a few months ago,” Mr. Bolton told Fox News on Sunday, but his administration is not “starry eyed about what may happen here.”
“I think it is going to happen; the dates and the places are still under discussion,” he said. “I think the president is eager to do it as soon as possible.”
On Friday, Mr. Kim and Mr. Moon signed a joint declaration recognizing “a nuclear-free Korean Peninsula” and “complete denuclearization” as a common goal of the two Koreas. But during the summit events, some of which were broadcast live around the world, Mr. Kim never publicly renounced his nuclear weapons.
Even in the additional details released on Sunday by South Korean officials, Mr. Kim appeared to hedge his bets, indicating that denuclearizing his country could be a long process that required multiple rounds of negotiations and steps to build trust. But he laid out a vague idea of what his impoverished country would demand in return for giving up its nuclear weapons.
”If we meet often and build trust with the United States, and if an end to the war and nonaggression are promised, why would we live in difficulty with nuclear weapons?” Mr. Kim was quoted as saying by South Korean officials.
Mr. Moon briefed Mr. Trump on the meeting during a call on Saturday, telling him that Mr. Kim had said that he and Mr. Trump could “get along well,” to which Mr. Trump responded that he “looked forward” to their meeting.
On Sunday, Mr. Moon also spoke with the Japanese prime minister, Shinzo Abe, to relay Mr. Kim’s willingness to open dialogue with Tokyo, which is threatened by the North’s nuclear weapons and missile development.
The peacemaking comments stand in stark contrast to previous remarks and actions by Mr. Kim, who drove the Peninsula close to the brink of war last year by undertaking a series of missile and nuclear tests.
He suddenly switched to diplomatic overtures this year, extending an offer to meet Mr. Trump, which, surprisingly, was accepted. A week ago, Mr. Kim announced an end to all nuclear and long-range missile tests and the closing of the nuclear test site in mountainous Punggye-ri, in northeast North Korea.
In the meeting on Friday, Mr. Kim and Mr. Moon also agreed to start talks this year with Washington to negotiate a peace treaty to formally end the 1950-53 Korean War, one of the key security guarantees that the North has long demanded.
But North Korea has so far offered no timeline for dismantling its nuclear weapons and facilities. Nor has it clarified how it defines a “nuclear-free Korean Peninsula,” and especially whether that means a withdrawal or significant reconfiguration of American troops based in South Korea, as it has demanded before.
Even before Mr. Moon met with Mr. Kim, South Korean officials said any joint statement was bound to be vague on the terms of denuclearization because Mr. Kim would try to settle critical issues directly with Washington.
If Mr. Kim intends to win a peace treaty, diplomatic recognition and billions of dollars in economic aid from Washington and its allies, as South Korean officials hope he does, trading away his nuclear arsenal is his biggest bargaining chip. He cannot reveal his hand too soon, South Korean officials said.
Skeptics fear that Mr. Kim does not really intend to give up his nuclear weapons and is merely trying to soften his image, escape sanctions and make it more difficult for Mr. Trump to continue to threaten military action. But South Korean officials argue that Mr. Kim is sincere in trading his nuclear weapons for a promise to end hostilities and get Washington’s help to improve his country’s economy.
North Korea’s promise to invite outsiders to Punggye-ri reflected “Mr. Kim’s determination to actively and pre-emptively deal with the process of verifying denuclearization,” Mr. Yoon said.
In another conciliatory gesture toward South Korea, Mr. Kim made his own pledge of nonaggression toward the South.
“I am determined not to repeat the painful history of the Korean War. As the same nation living on the same land, we should never shed blood again,” he told Mr. Moon, according to Mr. Yoon.
Mr. Kim even vowed to readjust his country’s clock to match the time zone in South Korea, which with the rest of the region run 30 minutes ahead of the North’s.
“When I was sitting in the waiting room, I saw two clocks on the wall, one of the Seoul time and the other of the Pyongyang time, and I felt bad about it,” Mr. Kim was quoted as telling Mr. Moon. “Why don’t we reunify our clocks first?”