A former military spy chief, Kim Yong Chol has been a central player in the recent thaw in relations between North Korea and South Korea, as well as the United States.

At the same time, the man who is basically the North Korean leader's chief of staff was spotted in the Beijing airport Monday en route to Singapore, the site of the potential summit.

Chung Sung-yoon, an analyst at the Korea Institute for National Unification, said Kim Yong-chol would be the most senior North Korean official to step onto USA soil since Vice Marshall Jo Myong-rok met then-president Bill Clinton in 2000.

Nauert provided no further details. The U.S. delegation reportedly included Sung Kim, U.S. ambassador to the Philippines and a former U.S. special representative for North Korea policy. The U.S. team was said to include Allison Hooker, a Korea specialist on the White House National Security Council (NCS), and Randall Schriver, the assistant secretary of defense for East Asian and Pacific security affairs.

The two sides are also expected to hold separate talks on protocol and security in Singapore on Tuesday, with a White House team leaving for Singapore on Sunday.

Earlier on Sunday, South Korean President Moon Jae-in said he and North Korea's Kim had agreed during a surprise meeting on Saturday that the North Korea-US summit must be held.

But it has been thrown into uncertainty, after Mr Trump said he would no longer be attending. Kim Jong Un agrees with me on this.

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"But since that letter that he called this thing off last week, the North Koreans are suddenly warming to the possibility of a meeting that could be back on right now", Baldwin said.

US President Donald Trump is yet to confirm on the summit.

Trump last week said he was pulling out of the scheduled June 12 meeting in Singapore, citing North Korea's "open hostility", but then said the talks could still happen. Analysts said the pressure from the top makes a meeting more likely.

Across Asia, administration officials have been dispatched to carry out Trump's directive. "It's good that the two will meet, and my hope is that would set the stage for more realistic, more direct, specific conversations later on".

The president made the comments in a tweet on Sunday as U.S. officials arrived in North Korea and met their counterparts at the border village of Panmunjom. In his Sunday press conference, Moon said that the meaning of denuclearization was a question the USA and North Korea needed to decide without South Korea's help. Libyan dictator Moammar Qaddafi was killed in an uprising several years later.

Moon on Sunday dodged a question on whether Kim clearly mentioned whether he would agree to the USA demand for complete, verifiable, irreversible denuclearization.

"If North Korea and the US are to have a summit, then their summit is possible only after they confirm each other's intention on that regard", Moon said. "It will happen!" Trump said in the same tweet.

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