HANOI, Vietnam — President Trump and Kim Jong-un, North Korea’s leader, abruptly ended their second summit meeting on Thursday when negotiations collapsed after the two sides failed to agree on even the first steps on nuclear disarmament, a peace declaration or reducing sanctions on the North.
“It was about the sanctions,” Mr. Trump said at an afternoon news conference in Hanoi, Vietnam, referring to Mr. Kim’s demand that the United States lift harsh economic sanctions imposed on North Korea with the approval of the United Nations. “Basically they wanted the sanctions lifted in their entirety, but we couldn’t do that.”
“Sometimes you have to walk,” Mr. Trump added.
The premature end to the negotiations means the diplomacy between the United States and North Korea that has gone on for most of a year remains stalled, even as experts say North Korea continues to produce fissile material to make nuclear warheads.
It also undermines the image Mr. Trump has long cultivated of himself as a tough negotiator who can bring adversaries into a deal.
Mr. Trump said that Mr. Kim had agreed to take an important step toward dismantling a central part of his nuclear program — the Yongbyon enrichment facility — but that Mr. Kim said he would do so only if all sanctions were lifted.
The president and Secretary of State Mike Pompeo said the North would have to dismantle other weapons systems before all sanctions were lifted. They added that the two sides would continue negotiations in other settings, and stressed that there were nuclear sites that the Americans are aware of but that are unknown to the public.
In response to a question, Mr. Trump also acknowledged that his administration was aware of a second enrichment site other than Yongbyon.
Mr. Trump had flown across the world to try to work face-to-face with Mr. Kim for the second time on the signature diplomatic initiative of his presidency, an effort to reduce what American officials regard as one of the world’s foremost nuclear threats. Experts estimate that the North has 30 to 60 nuclear warheads and possibly a ballistic missile that can hit the continental United States.
If, as Mr. Trump said, Mr. Kim insisted that the United States lift all economic sanctions in exchange for just the dismantlement of Yongbyon, that was a severe misreading of the American strategy. American officials have said that the sanctions are their main leverage with North Korea, and that keeping them tight is critical to the goal of full denuclearization.
There was talk before Thursday that the Americans might allow more economic exchange between South Korea and the North as part of a deal, but that probably would have been as far as alleviation of sanctions would have gone at this point.
The collapse of the talks came in the shadow of withering congressional testimony in Washington by Michael D. Cohen, Mr. Trump’s former lawyer, who spent hours on Wednesday describing Mr. Trump’s lies and deep character flaws.
Asked at the news conference about Mr. Cohen, Mr. Trump said, “He lied a lot.”
“I think having a fake hearing like that and having it in the middle of this very important summit is really a very terrible thing,” Mr. Trump said, alluding to his earlier criticism that the hearing had been organized for partisan purposes by the Democratic-controlled House of Representatives.
Mr. Trump said Mr. Cohen had indicated in testimony that he did not know of any collusion between Mr. Trump and the Russian government.
After the talks with Mr. Kim collapsed and before Mr. Trump spoke to reporters, the White House issued a statement saying that Mr. Trump and Mr. Kim had “discussed various ways to advance denuclearization and economic driven concepts,” and that they had had “very good and constructive meetings,” but that “no agreement was reached at this time.”
Officials from both sides had hoped the Hanoi summit meeting would produce more concrete results than the vague communiqué issued by the two leaders issued after their first meeting last June, in Singapore.
Back then, they said they would work on four points: improving relations, establishing a “lasting and stable peace regime” on the Korean Peninsula, affirming that Pyongyang would work toward “complete denuclearization” of the peninsula, and the mutual return of remains from soldiers killed in the Korean War.
Since then, American national security officials have emphasized that denuclearization was their most important goal, while North Korea has pushed for improving relations with the United States and South Korea first.
The administration of President Moon Jae-in of South Korea appears to have agreed with Mr. Kim that establishing a more stable peace is the first priority, and it has been moving much faster than the United States in opening up diplomatically to the North.
“It is regrettable that they could not reach a complete agreement,” Kim Eui-kyeom, a spokesman for Mr. Moon, said after news emerged of the diplomatic breakdown on Thursday. “But it also seems clear that both sides have made more significant progress than ever.”
The collapse of the talks was a stark departure from the earlier mood of the two-day gathering. On Thursday morning, Mr. Trump and Mr. Kim kicked off the day by meeting one-on-one at the Metropole Hotel, where they had had an intimate dinner the previous night.
From the start, Mr. Trump emphasized that getting North Korea to dismantle its nuclear weapons program could be a lengthy effort, and that it would be coupled with attempts to integrate the isolated nation into the global economy.
The Trump administration has kept up harsh sanctions on North Korea. In 2017, the administration persuaded the United Nations Security Council — including China and Russia, allies of North Korea — to impose three rounds of sanctions on the North that, in total, were much harsher than sanctions pushed by prior administrations.
And before the collapse of Thursday’s talks, Mr. Trump was cautioning patience.
“I’ve been saying very much from the beginning that speed is not that important to me,” he said at the beginning of Thursday’s meetings. “I very much appreciate no testing of nuclear rockets, missiles.”
North Korea last did a nuclear test in September 2017 and a ballistic missile test in November 2017.
Mr. Trump mentioned potential economic growth in North Korea three times in his brief morning comments, saying that the country would become an “economic powerhouse.”
The message from the morning seemed clear — that integrating North Korea into the global economy would help moderate the country’s behavior and bring it closer to the American orbit. Mr. Trump appeared ready to gamble that as long as Mr. Kim and other North Korean officials rid themselves of any intent to harm the United States, they could keep their nuclear capability for a while.
Mr. Kim, when asked by an American reporter whether he was ready to denuclearize, said, “If I’m not willing to do that, I wouldn’t be here right now” — to which Mr. Trump replied, “That might be the best answer you’ve ever heard.”
Mr. Kim also suggested that he would accept an American liaison office in his country.
Earlier, the two leaders took a stroll by the pool, then went into the hotel restaurant to chat privately. Separately, Mr. Pompeo spoke to his North Korean counterpart, Kim Yong Chol, a top Communist Party official and former spy chief.
Mr. Pompeo has been anxious about letting Mr. Trump have too much time alone with Mr. Kim, wary that the president would make snap concessions without proper consultation with his top national security advisers.
During Mr. Trump’s Thursday afternoon news conference after the collapse of the talks, the president said that he could have signed a deal, but that Mr. Pompeo was not satisfied with the terms. Mr. Pompeo has taken the lead in the diplomatic talks and is more skeptical of Mr. Kim’s intentions than Mr. Trump is.