TOKYO — It’s all China’s fault, at least according to President Trump, who again blamed Beijing late Wednesday for an impasse in negotiations with Pyongyang over its nuclear and missile programs.

But several experts said the real problem lies much closer to home, in Trump’s casual approach to negotiations with the North Koreans and the vague, oral promises exchanged at his meeting with the North Korean leader in Singapore in June.

Citing multiple individuals familiar with the negotiations, Vox reported Wednesday that Trump told Kim Jong Un in Singapore that he would sign a declaration to end the Korean War soon after their meeting.

Since then, the Trump administration has repeatedly asked Pyongyang to first dismantle most of its nuclear arsenal. That explains the current stalemate in negotiations, Vox reported.

“If that’s true, that’s why the North Koreans are dragging their feet,” said Robert Kelly, a professor of political science at Pusan National University in South Korea. “That’s Trump’s blunder.”

North Korea believes that Trump made the same promise — to declare an end to the war — to Kim Yong Chol, a top North Korean official close to Kim Jong Un, at the White House on June 1 — 11 days before the summit, Vox also reported.

“The bill comes due,” tweeted Vipin Narang, an associate professor of political science at MIT.

“This was exactly the risk of Trump freelancing in Singapore: making promises to Kim Jong Un (and earlier Kim Yong Chol) that the Administration could not and would not deliver on. “

“Things may quickly heat back up, and this one is squarely on Trump,” he added.

Secretary of State Mike Pompeo, by contrast, has asked Pyongyang to surrender 60 to 70 percent of its nuclear warheads in six to eight months, according to Vox, explaining why he was greeted with such hostility in North Korean state media.

Trump’s decision to call off Pompeo’s latest trip to Pyongyang came after the North Koreans warned in a letter to Pompeo last week that talks with the United States risked falling apart, as first reported by The Washington Post’s Josh Rogin.

“They basically don’t think we’re doing enough,” a senior U.S. official told Reuters. He said the tone of the letter was “if you’re not willing to give something, then don’t come.”

President Trump meets with North Korean leader Kim Jong Un on Sentosa Island, in Singapore, in June. (Evan Vucci/AP)

Rogin said the idea of declaring an end to the war faced significant internal opposition within the administration, particularly from national security adviser John Bolton and Defense Secretary Jim Mattis.

Suh Hoon, director of South Korea’s National Intelligence Service, told a closed-door parliamentary hearing Tuesday that Pompeo’s trip was canceled over the competing demands from the two sides.

“As determined by the NIS, he is unable to go because North Korea’s demand for the end-of-war declaration clashed with the U.S. urging that denuclearization be declared first,” Suh was quoted as saying by lawmaker Kim Min-ki.

In July, North Korea’s Foreign Ministry issued a statement underlining how important it considered a declaration of an end to the war in “defusing tension and establishing a lasting peace regime on the Korean Peninsula,” as well as creating trust between the two nations. “President Trump, too, was more enthusiastic about this issue at the DPRK-U.S. summit talks,” an unnamed spokesman was quoted as saying, referring to North Korea by the initials of its official name.

A similar statement in August complained that the United States had issued a “unilateral and gangster-like demand for denuclearization” while threatening to “backtrack on the issue it had agreed on to end the status of war under certain conditions and excuses.” It also mentioned Trump’s alleged enthusiasm for the step.

The Korean War ended in 1953 with an armistice, not a formal peace agreement. A declaration of an end to the war is seen by its supporters as a way to signal of an end to hostilities between the two Koreas and between North Korea and the United States. But it would be only a first step toward a full peace treaty involving the complete denuclearization of the Korean Peninsula. Skeptics argue it would give the North Koreans too great a reward without securing any real progress on dismantling their nuclear program and could ultimately undermine the U.S.-South Korea military alliance.

South Korean efforts to persuade Washington and Pyongyang to move simultaneously on the two steps have so far foundered, the Atlantic reported this week.

Pusan National University’s Kelly said Trump offered the North Koreans a huge amount in Singapore, including the suspension of military exercises with South Korea, without getting concrete promises in return.

His lack of understanding of the issues and lack of attention to detail have finally “collided with the reality of North Korea,” Kelly said. “They are not going to completely denuclearize ever. Nobody actually believes that. They took years developing these weapons. They are not going to give them up because Donald Trump says some stuff on Twitter.”

At his news conference after the Singapore summit, Trump was asked about the possibility of a peace agreement to formally end the Korean War.

“What we signed today had a lot of things included,” he said. “You had things that were not included that we got after the deal was signed.”

When he called off Pompeo’s planned visit last week, Trump blamed a lack of progress toward denuclearization, but he also said China was not helping as much as in the past because of the trade dispute between Beijing and Washington. It was a theme he returned to Wednesday.

“I would imagine the trade war with China isn’t helping,” Kelly added. “I would imagine the Chinese aren’t being helpful, and that probably hurts at the margins, but the real problem is the incompetence of the Trump administration.”

China’s Foreign Ministry called Trump’s comments “irresponsible” and hard to understand, Reuters reported. Foreign Ministry spokeswoman Hua Chunying told a regular news conference that China could not accept “the various ways” Trump tried to pin the blame on Beijing.

“We hope that the United States will value integrity and keep its commitments like China did, and play a positive, constructive and responsible role in promoting the process of political settlement of the peninsula issue,” she said, according to the Global Times.

Meanwhile, the breakdown in talks has forced the government in Seoul to recalibrate, experts said.

South Korean media have reported on mounting speculation that the proposed opening of a joint inter-Korean liaison office inside North Korea, supposed to take place in August, might be delayed — although the government has said only that consultations are still underway.

Seoul is likely to interpret Mattis’s comment that the United States suspended only some military exercises with South Korea — not its entire program — as a warning “not to get ahead of itself in cooperation with the North,” said Shin Beom-chul, director of the Center for Security and Unification at the Asan Institute for Policy Studies in Seoul.

“Despite wanting to speed up diplomacy with Pyongyang, Seoul cannot but moderate the pace in this situation,” Shin said. He added that South Korean President Moon Jae-in is bound to take a “more prudent approach” toward deeper economic cooperation with the North when he visits Pyongyang in September.

Min Joo Kim in Seoul and Liu Yang in Beijing contributed to this report.