USA and North Korean officials met Sunday at the Korean demilitarized zone, and White House deputy chief of staff Joe Hagin and others from the Trump administration flew to Singapore, the planned site for the summit.
The flurry of diplomatic activity intensified Tuesday after South Korean media reported that Kim Yong Chol's name was on the passenger list for a fight Wednesday from Beijing to NY.
Kim Yong Chol, a four-star general who has been at the forefront of North Korea's diplomatic outreach, landed at Beijing Capital International Airport on Tuesday, according to television footage from the airport.
Trump tweeted: "We have put a great team together for our talks with North Korea". As Kim and Pompeo were meeting in NY, other USA teams were meeting with North Korean officials in Singapore and in the heavily fortified Korean Demilitarized Zone.
General Kim Yong-chol, 72, has emerged as a key player in North Korean diplomacy in the first half of 2018.
Trump tweeted earlier on Tuesday that the senior North Korean official was en route to the US, calling the visit a "solid response" to his letter.
Kim, one of North Korean leader Kim Jong Un's most trusted aides, is a former military intelligence chief and now a vice chairman of the ruling party's central committee.
Trump did not detail what he meant by "my letter;" he could have been referring to the missive he disclosed last week calling off the Kim meeting that had been scheduled for June 12 in Singapore.
U.S. Secretary of State Mike Pompeo tapped veteran American diplomat Sung Kim to handle pre-summit negotiations. American officials are now in North Korea to meet their counterparts in the truce village of Panmunjom on demilitarized land near the South Korean border.
Led by Sung Kim, the USA ambassador to the Philippines and former U.S. ambassador to Seoul, the United States officials first met their counterparts including Choe Son-hui, North Korea's vice foreign minister, on Sunday.
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If Trump is unable to negotiate those weapons away and unwilling to live in a world where North Korea poses a nuclear threat, then "you're going to have to do something to go after them at some point", the senator said. Earlier this month, Gen. Kim met with Secretary of State Mike Pompeo in Pyongyang, hours before North Korea released three American prisoners.
Both Trump and Abe are set to attend the Group of Seven economic summit June 8-9 in Canada, but the two may meet at the White House prior to that, according to officials in Washington and Tokyo.
Senior Trump administration officials are also coordinating directly with North Korean counterparts at the Korean demilitarized zone and in Singapore, Sanders said.
Sung Kim will meet North Korea's foreign ministry official Choi Sun Hee again on Wednesday at the DMZ, Yonhap reported on Tuesday, citing a diplomatic source, adding that the agenda for the Trump-Kim summit would roughly be decided at the meeting.
In Washington, lawmakers and former USA intelligence officials expressed general support Sunday for proceeding with the summit, but many reacted skeptically to North Korea's suggestion that it is open to discussing denuclearization.
Kim and Pompeo are expected to hold extensive talks on big deals related to the North's denuclearization roadmap and security assurances for Pyongyang.
North Korean leader Kim Jong Un's de facto chief of staff, Kim Chang Son, meanwhile, flew to Singapore via Beijing late on Monday, Japanese public broadcaster NHK reported.
Since the 1970s, the United States and South Korea have been holding a major summertime exercise called Ulchi Freedom Guardian that involves tens of thousands of troops.
The talks are focused on what would be the substance of a potential summit between Trump and Kim - the issue of North Korea's nuclear weapons program. "What's uncertain for Kim is not his intention to denuclearize, but the US stance in hostile relations with North Korea and whether the USA can really secure and guarantee his regime".