HANOI, Vietnam — U.S. negotiators are no longer demanding that North Korea agree to disclose a full accounting of its nuclear weapons and ballistic missile programs as part of talks this week between President Donald Trump and Kim Jong Un, according to current and former senior U.S. officials.

The decision to drop, for now, a significant component of a potential nuclear deal suggests a reality that U.S. intelligence assessments have stressed for months is shaping talks as they progress: North Korea does not intend to fully denuclearize, which is the goal Trump set for his talks with Kim.

Disclosure of a full, verifiable declaration of North Korea’s programs is the issue over which the last round of serious negotiations between Pyongyang and world powers, including the U.S., fell apart a decade ago.

Negotiations between U.S. and North Korean officials in advance of Trump and Kim’s second summit, which begins Wednesday night over dinner in Hanoi, have focused heavily on a core component of Pyongyang’s program, the Yongbyon nuclear reactor, officials said. Dr. Siegfried Hecker, a nuclear scientist who has visited the Yongbyon Nuclear Scientific Research Center numerous times to assess the country's capabilities, said dismantling elements of the facility would be the most significant step North Korea could take toward denuclearization.

“Yongbyon is the heart of North Korea’s nuclear program,” Hecker said, explaining that completely dismantling the reactor there would be critical and would mean North Korea would never be able to make plutonium there again.

The White House did not respond to a request for comment.

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The Trump administration is hoping to get a significant concession from North Korea on Yongbyon, but it’s unclear if the U.S. can offer something in exchange that Kim would accept. North Korea wants sanctions relief, and U.S. officials have advised the president against taking such a step at this stage in negotiations. North Korea has offered to freeze activity at Yongbyon in past rounds of negotiations with previous U.S. administrations.

Current and former U.S. officials note that North Korea has other sites with similar capabilities, however, and they are raising concerns that Pyongyang won’t negotiate on all aspects of its weapons programs if it’s not forced to disclose them.

In recent months researchers have discovered that North Korea has as many as 20 undisclosed ballistic missile sites, according to Beyond Parallel, a project sponsored by the Center for Strategic and International Studies, a defense think tank. One of the sites is the Sino-ri Missile Base about 130 miles north of the demilitarized zone between North Korea and South Korea, where about 28,000 U.S. troops are stationed.

North Korea hasn’t launched a missile test since engaging diplomatically with the U.S. last year, but it has continued to otherwise refine and advance its nuclear weapons program in the months since Trump first met with Kim last June in Singapore, U.S. officials have said.

Secretary of State Mike Pompeo, who had been leading negotiations until he named a special envoy to focus on the effort, has grown increasingly concerned about the prospects of reaching a deal with North Korea that gets rid of its nuclear threat, current and former senior U.S. officials said.

Last August Pompeo named a special envoy to lead the North Korea talks, Stephen Biegun. Some White House and State Department officials have raised concerns in recent days that Biegun could be offering too much from the U.S. to his North Korean counterparts.

Officials point out that the outcome of the summit on Wednesday and Thursday is difficult to predict because Trump could get into the room with Kim and ignore his advisers' recommendations based on preliminary negotiations between U.S. and North Korean officials. Trump has styled himself since his presidential campaign as a master negotiator and dealmaker who relies on his instincts over experts and research. He told the Washington Post in an interview last fall that “my gut tells me more sometimes than anybody else’s brain can ever tell me.”

Putting off a requirement that North Korea will disclose the entirety of its weapons programs does not mean the U.S. has dropped the demand entirely. Some officials say it would be addressed later.

But some current and former U.S. officials have argued that such a declaration should be gained early in talks given the intelligence assessment that Kim does not intend to denuclearize and that North Korea has a history of concealing sites.

Officials add that even if North Korea provided a list of locations, it wouldn’t make much of a difference because a dismantling of them would require a vigorous verification process to which Kim is unlikely to agree. There haven’t been any inspectors on the ground in North Korea during the current talks.

Hecker said allowing inspectors in would also be a significant step for the North Koreans. “Letting inspectors look at the testing tunnels” would be an important step forward, he said.

Carol E. Lee reported from Hanoi, and Courtney Kube from Washington.