It was the clearest sign yet that the on-again-off-again summit between Trump and Kim is likely to be held as initially agreed, in Singapore on June 12.

The unannounced meeting at the Panmunjom border village between Moon and Kim came a month after they held the first inter-Korean summit in more than a decade at the same venue and declared they would toward a nuclear-free Korean peninsula.

"The two leaders candidly exchanged views about making the North Korea-U.S. summit a successful one and about implementing the Panmunjom Declaration," South Korea's presidential spokesman said in a statement.

Moon, who returned to Seoul earlier this week after a meeting with Trump, will announce details of the meeting with Kim on Sunday morning.

Read: N. Korea Says Still Open to Talks after Trump Kim Summit Canceled

Trump said on Friday that Washington was having "productive talks" with Pyongyang about reinstating the June 12 meeting, just a day after canceling it.

Politico magazine reported that an advance team of 30 White House and State Department officials was preparing to leave for Singapore later this weekend.

Reuters reported earlier this week the team was scheduled to discuss the agenda and logistics for the summit with North Korean officials. The delegation was to include White House Deputy Chief of Staff Joseph Hagin and deputy national security adviser Mira Ricardel, U.S. officials said, speaking on condition of anonymity.

Trump said in a Twitter post late on Friday: "We are having very productive talks 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 had earlier indicated the summit could be salvaged after welcoming a conciliatory statement from North Korea saying it remained open to talks.

"It was a very nice statement they put out," Trump told reporters at the White House. "We'll see what happens - it could even be the 12th."

"We're talking to them now. They very much want to do it. We'd like to do it," he said.

The comments came just a day after Trump canceled the meeting, citing Pyongyang's "open hostility."

REUTERS