Thomas Maresca

Special to USA TODAY

SEOUL – North Korea has not taken “concrete steps” to dismantle its nuclear weapons program, Vice President Mike Pence told a group of U.S. diplomats on Wednesday.

Speaking to about 180 U.S. ambassadors at a conference in the State Department, Pence said Pyongyang has not yet begun to fulfill its pledge for complete denuclearization made in a summit between President Donald Trump and North Korean leader Kim Jong Un last June in Singapore.

"While the president has started a promising dialogue with Chairman Kim, we still await concrete steps by North Korea to dismantle the nuclear weapons that threaten our people and our allies in the region," Pence said.

The vice president’s remarks came amidst growing signs that a second summit between Trump and Kim is in the works. North Korea’s top nuclear negotiator, Kim Yong Chol, is expected to arrive in Washington, D.C., on Thursday ahead of a meeting with Secretary of State Mike Pompeo, a South Korean newspaper and other media outlets reported Wednesday.

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Kim Yong Chol will be carrying a new letter from Kim Jong Un for Trump, according to a CNN report citing a source familiar with the negotiations.

The State Department and the U.S. Embassy in Seoul would not confirm the meeting as of Wednesday night.

Trump has also teased an upcoming summit, saying recently that negotiations were already underway for a location and that the result would be announced “in the not-too-distant future.”

Speculation has increasingly focused on Vietnam as the preferred location for the summit, with a report from a South Korean newspaper last week claiming U.S. and North Korean officials have already met in Hanoi to discuss scheduling the summit.

Also, Japan’s Yomiuri Shimbun newspaper reported on Sunday that U.S. has proposed to the North to hold the talks in Vietnam in mid-February.

Washington has suggested Vietnam, a communist nation with a rapidly developing economy, could serve as a model for North Korea.

During a visit to Hanoi in July, Pompeo called on North Korea to replicate Vietnam’s economic “miracle.”

A second Trump-Kim summit would seek to push forward a diplomatic process that has slowed since their historic Singapore meeting.

That summit produced a declaration that North Korea would work toward a “complete denuclearization of the Korean peninsula,” but details and a timeline for carrying out the agreement have remained vague.

Pyongyang is looking for relief of punishing international sanctions in exchange for steps it has already taken, such as dismantling a nuclear testing site, while Washington is holding out for complete denuclearization.

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South Korean foreign minister Kang Kyung-wha told reporters Wednesday that Seoul and Washington have been closely discussing what “corresponding measures” could be taken in response to the North’s progress on denuclearization. Incentives could include a formal declaration of the end of the 1950-1953 Korean War, humanitarian assistance and a communications channel with the U.S., she said.

Kang said that anticipation for a second North Korea-U.S. summit is rising and that nuclear negotiations “are expected to resume quickly.”

North Korea didn’t launch any missiles or test any nuclear weapons in 2018, and in May, Pyongyang made a show of dismantling its Punggye-ri nuclear test site. But international inspectors have not been allowed to visit the site, and research shows that the communist state continues to develop its ballistic weapons program at several locations.

A report released last week by North Korea analysis website 38 North said that the country’s Yongbyon nuclear facility remains operational and well-maintained but does not appear to be currently in use. The site produces the fissile material used as fuel for nuclear weapons.