The Washington Post first reported the visit of the US delegation led by Amb. Sung Kim, a former US ambassador to South Korea and former negotiator on North Korea's nuclear weapons program. The State Department later confirmed that the two sides were having talks in the truce village of Panmunjom, which sits on the inter-Korean border.

"I truly believe North Korea has brilliant potential and will be a great economic and financial Nation one day," Trump wrote.

"Kim Jong-un agrees with me on this. It will happen!"

The US president has increasingly offered economic rewards in exchange for denuclearization, although the exact terms of any deal are unclear.

Washington seeks a complete, verifiable and irreversible dismantlement of the North's nuclear weapons program, but Pyongyang has rejected demands for "unilateral" denuclearization and threatened to pull out of the summit if such discussions continue.

Kim has been quoted as offering a phased and synchronized process that would likely involve a gradual give and take of dismantlement steps in exchange for sanctions relief.

Last week the North demolished its nuclear test site in Punggye-ri in front of a small group of international journalists.

A few hours later, Trump abruptly canceled the summit, citing "tremendous anger and open hostility" in recent North Korean comments.

Apparently eager to salvage the rare opening for diplomacy, the North responded that it was still ready to meet with the US at any time. And Trump welcomed the "warm and productive" statement, saying the summit could go ahead as planned.

In the meantime, South Korean President Moon Jae-in and Kim held a second meeting in Panmunjom Saturday.

Moon later announced that Kim had reaffirmed his commitment to denuclearization and willingness to meet with Trump.

The White House said Saturday that a "pre-advance team" was headed to Singapore to prepare for the summit should it take place. (Yonhap)