WASHINGTON, May 28 (NNN-Bernama) -- US ambassador Sung Kim on Sunday crossed into North Korea to make preparation for the meeting between North Korean leader King Jong Un and US President Donald Trump, Xinhua news agency reported, citing a newspaper report.

Sung Kim, a former US ambassador to South Korea and former nuclear negotiator, was summoned from his present posting as US ambassador to the Philippines for talks with Choe Son Hui, North Korea's vice foreign minister, the Washington Post said.

Sung Kim met with Choe Son Hui accompanied by Allison Hooker, the US National Security Council member, and Randall Schriver, the assistant secretary of defence for East Asia of State Department.

The Washington Post quoted State Department spokesperson Heather Nauert as saying the meetings are expected to continue Monday and Tuesday in the northern part of the demilitarised zone where North Korean leader Kim Jong Un met with South Korean President Moon Jae-in on Saturday.

The two delegations will reportedly focus on the substance of the summit between Donald Trump and Kim Jong Un -- North Korea's nuclear weapon programme.

The White House has not confirmed the report.

A day before, Moon and Kim held a surprise meeting on the northern side of the border village Panmunjom, the second inter-Korean summit in a month.

Moon said on Sunday that both Kim and Trump wished the success of their summit "wholeheartedly." Trump also said on Saturday that Washington is "doing very well in terms of the summit with" Kim.

"A lot of people are working on it. We're looking at June 12 in Singapore. That hasn't changed, and its moving along pretty well," said Trump.

Trump scrapped the scheduled meeting on Thursday, saying that it will not happen "based on the tremendous anger and open hostility" displayed by statements from North Korea.

However, he reversed course just one day after the announcement saying that both sides wanted the meeting to happen and it could still go ahead as scheduled.

A White House spokeswoman said on Saturday that a White House team will leave for Singapore this weekend to prepare for the Trump-Kim talks on June 12.--NNN-BERNAMA