TOKYO — Secretary of State Mike Pompeo met in Pyongyang on Friday with a senior North Korean official in an effort to breathe new life into nuclear negotiations that have come under intense scrutiny amid U.S. intelligence reports that cast doubt on the isolated regime’s willingness to relinquish its nuclear and missile arsenal.

The top U.S. diplomat is under pressure to show progress after the June meeting between President Trump and North Korean leader Kim Jong Un in Singapore, at which the two sides agreed to work toward the “complete denuclearization of the Korean Peninsula.”

In the weeks since the meeting, U.S. and North Korean officials have struggled to maintain basic communication, North Korea has not returned the remains of U.S. soldiers who went missing during the Korean War as promised, and new satellite imagery has shown the regime expanding a key missile-manufacturing plant.

Still, Pompeo sounded a note of optimism as he sat down with his main interlocutor, Kim Yong Chol, a vice chairman of North Korea’s Central Committee and former spy chief who has resisted U.S. efforts to spell out a detailed understanding of what denuclearization would look like.

“I count on [this meeting] being very productive,” Pompeo said.

Sitting at a large square table, Kim Yong Chol welcomed the U.S. delegation, which includes officials from the CIA, State Department, Pentagon and White House. “Today’s meeting is a really meaningful meeting,” he said.

The two delegations met Friday at a guesthouse complex a short drive from the massive mausoleum where former leaders Kim Il Sung and Kim Jong Il are interred.

Managing expectations for its North Korea diplomacy has been a challenge for the Trump administration, with the White House touting historic progress amid more cautious remarks from the State Department.

National security adviser John Bolton, a longtime North Korea hawk, said Sunday that Pompeo would deliver a plan to Kim Jong Un for the complete dismantlement of Pyongyang’s nuclear program in one year. But on Tuesday, State Department spokeswoman Heather Nauert clarified that the United States was not imposing a timeline. Pompeo has said dismantlement could take 2½ years.

Meanwhile, Trump has said North Korea no longer poses a nuclear threat, and on Thursday he claimed credit for preventing war on the Korean Peninsula.

“When I took office and under the Obama administration, North Korea was doing tremendous testing, tremendous missile launches, and you can ask President Obama — he was very close to going to war,” Trump told reporters on Air Force One. “I don’t think enough credit’s given to the fact that under the Obama administration it was a mess. There was no talk — it was only nuclear testing and rocket launches. And we haven’t had that for eight months.”

Since Kim took power in 2011, he has launched more than 85 missiles and conducted four nuclear weapons tests. Under Trump’s tenure, there have been nine missile launches, at least two involving intercontinental ballistic missiles, a major breakthrough, and its largest nuclear weapons test.

A pause in North Korean launches and testing was also achieved during the Obama administration for more than a year while Pyongyang promised the denuclearization of the Korean Peninsula, an outcome it never delivered on.

The mixed messaging inside the Trump administration has been taken as an indication that the United States may be backing off its original demand that North Korea completely dismantle its nuclear program before receiving any sanctions relief.

On Thursday, the State Department denied any change in Washington’s negotiating position.

“Nothing could be further from the truth,” Nauert said in a statement. “Our policy toward North Korea has not changed. We’re committed to a denuclearized North Korea.”

But the department has made a subtle tweak to its demand of North Korea after originally calling for “complete, verifiable, and irreversible denuclearization,” or CVID. In the past week, it has not used the CVID language, instead calling on North Korea to carry out “final, fully verified denuclearization.”

Concerns about North Korea’s sincerity have risen as even basic goodwill gestures that Pyongyang agreed to in Singapore have not been realized, such as its statement promising the “immediate repatriation” of the remains of fallen U.S. soldiers who were lost during the Korean War.

Last month, Trump told a crowd of supporters that 200 human remains had already “been sent back,” but U.S. military officials later said that was not the case.

The U.N. Command has at least one phone “hotline” open at the demilitarized zone splitting the two Koreas while waiting to receive the remains of U.S. service members, but there has been no communication at all yet with the North Koreans, said a U.S. defense official, speaking on the condition of anonymity because of the sensitivity of the situation.

The remains could be returned at the DMZ or at one of two military installations in South Korea — Osan Air Base in Pyeongtaek and Yongsan Garrison in Seoul, the official said.

“There was no concrete talk to arrange the details. . . . Wheels are just turning slower than perhaps what everyone thought,” the official said.

The Pentagon is “waiting on the diplomatic thing to jar loose something actionable,” the official added.

The remains issue is supposed to be the easy part. Experts have warned that verifying and removing Pyongyang’s nuclear weapons program, a challenge that has bedeviled successive U.S. administrations, could easily take 10 years, even assuming full North Korean compliance. Last week, The Washington Post reported that U.S. intelligence officials, citing newly obtained evidence, have concluded that North Korea does not intend to fully surrender its nuclear stockpile and instead is considering ways to conceal the number of warheads and secret production facilities it has.

Diplomats familiar with the talks, who also spoke on the condition of anonymity to describe the sensitive discussions, said the two sides have not even begun to form a shared understanding of what denuclearization would look like.

The State Department says Pompeo will try to get a better sense of that during his meetings with Kim Yong Chol, but in recent weeks U.S. officials have expressed frustration with the senior North Korean official for what they view as his inability or unwillingness to negotiate or act outside the scope of very limited orders from Kim Jong Un.

South Korean media had reported that Kim Yong Chol could be replaced in his chief negotiating capacity by the minister of foreign affairs, Ri Yong Ho, but Kim Yong Chol’s presence at key meetings on Friday suggested that his position is safe for now.

Dan Lamothe, Karen DeYoung and Anne Gearan in Washington contributed to this report.