SEOUL, South Korea >> Diplomacy accelerated Tuesday ahead of a potential summit between President Donald Trump and North Korean leader Kim Jong Un as a team of American diplomats involved in preparatory discussions left a Seoul hotel, possibly to continue talks with their North Korean counterparts.

Meanwhile, in Beijing, South Korea’s Yonhap news agency reported that senior North Korean official Kim Yong Chol planned to head to the United States, potentially for more talks to set up the summit. He would be the most senior North Korean official to visit the United States in 18 years.

Yonhap said Kim Yong Chol’s name was on the passenger list for a flight Wednesday from Beijing to New York. It earlier reported that he was heading straight to Washington, but later said he changed his flight to New York. South Korean officials couldn’t immediately confirm the report. Kim was seen in the Beijing airport Tuesday by The Associated Press.

Kim is a former military intelligence chief and now a vice chairman of the North Korean ruling party’s central committee tasked with inter-Korean relations. A visit to the United States would mark the highest-level North Korean official visit since 2000, when late National Defense Commission First Vice Chairman Jo Myong Rok visited Washington, South Korea’s Unification Ministry said.

In South Korea, it wasn’t immediately clear whether the American officials, including Sung Kim, the U.S. ambassador to Manila, were heading to the Korean village of Panmunjom, which straddles the border inside the Demilitarized Zone, where they met with North Korean officials on Sunday. Sung Kim is a former U.S. ambassador to South Korea and was a top negotiator with North Korea in past nuclear talks.

Trump withdrew from a planned June 12 summit with Kim Jong Un last Thursday, citing hostile North Korean comments, but has since said the meeting in Singapore could still happen. South Korean President Moon Jae-in, who has lobbied hard for nuclear negotiations between Trump and Kim, met with the North Korean leader in a surprise meeting on Saturday in an effort to keep the summit alive.

In their second meeting in a month, Moon said Kim expressed willingness to cooperate to end confrontation and work toward peace for the sake of a successful summit with Trump. But Kim also said he was unsure whether he could trust the United States over its promise to end hostile policies against North Korea and provide security assurances if the country does abandon its nuclear weapons, according to Moon.

Despite Kim’s apparent eagerness for a summit with Trump, there are lingering doubts about whether he will fully relinquish his nuclear weapons, which he may see as his only guarantee of survival. Moon has insisted Kim can be persuaded to abandon his nuclear facilities, materials and bombs in a verifiable and irreversible way in exchange for credible security and economic guarantees.

U.S. and South Korean officials haven’t confirmed the details of the pre-summit negotiations between Washington and Pyongyang at the border.

The officials may discuss bridging the gap between Washington and Pyongyang on what a deal on the North’s nuclear weapons would look like. There’s also speculation that American officials are trying to persuade the North Koreans to export a certain number of its nuclear warheads overseas at an early stage as proof of its commitment to denuclearize.

U.S. officials have talked about a comprehensive one-shot deal in which North Korea eliminates its nukes first and receives rewards later. But Kim, through two summits with Chinese President Xi Jinping in March and May, has called for a phased and synchronized process in which every action he takes is met with a reciprocal reward from the United States.

Seoul has been advocating an alternative approach in which the North’s comprehensive commitment and credible actions toward denuclearization are followed by a phased but compressed process of inspection and verifiable dismantling. Before he canceled the summit, Trump did not rule out an incremental approach that would provide incentives along the way to the North.