This team is focused on the substance of any summit between the two leaders - the issue of North Korea's nuclear weapons program.

After Saturday's surprise inter-Korean talks, South Korean President Moon Jae-in said Kim was still committed to the "complete denuclearisation" of the Korean Peninsula. But Moon declined to define "complete denuclearisation", suggesting that there are still fundamental gaps on the key issue bedevilling preparations.

Still, Moon, who is playing something of a mediator role in the talks, was optimistic. "We two leaders agreed the June 12 North Korea-US summit must be successfully held," he said Sunday.

The US team preparing for the talks travelled Sunday to Tongilgak, or "Unification House", the building where Kim met Moon on Saturday for impromptu talks aimed at salvaging the summit.

After North Korean officials, including Choe, lashed out at Vice President Mike Pence and national security adviser John Bolton, Trump abruptly announced that he was cancelling the talks, citing North Korea's "tremendous anger".

But after a magnanimous statement from North Korea on Friday, which said Kim still hoped to meet Trump "at any time", the summit appears to be on again.

"We are having very productive talks with North Korea about reinstating the Summit which, if it does happen, will likely remain in Singapore on the same date, June 12th., and, if necessary, will be extended beyond that date," Trump tweeted Friday night.

The White House has said that preparations will continue while the final decision on whether to proceed with the summit, scheduled to be held in Singapore, is made.

Trump confirmed Saturday that working-level meetings were continuing. "As you know there are meetings going on as we speak in a certain location which I won't name, but you'd like the location," he told reporters in Washington.

A separate US team led by Joe Hagin, deputy chief of staff in the White House, is organising logistics with Kim Chang-son, who is effectively the North Korean leader's chief of staff.

Kim Chang-son was in Beijing from Thursday to Saturday, according to Japanese and South Korean media reports, although it was not clear whether his trip was related to the summit preparations.

The Washington Post