TOKYO (REUTERS, XINHUA) - A top aide to North Korean leader Kim Jong Un arrived in Singapore on Monday night (May 28), Japanese public broadcaster NHK said on Tuesday, the latest indication that the on-again, off-again summit with US President Donald Trump is going ahead.

Kim Chang Son, Kim's de facto chief of staff, flew to Singapore via Beijing on Monday night, the report said.

At the same time, a team of US government officials, including the White House deputy chief of staff for operations Joe Hagin, left US Yokota Air Base in Japan for Singapore on Monday, NHK said.

The White House said a "pre-advance" team was travelling to Singapore to meet with the North Koreans.

A team of US officials, with a fleet of idling vehicles on standby, was at a hotel on the resort island of Sentosa but declined to comment.

On Tuesday, Kim Chang Son was also seen stepping out of the Fullerton Hotel and leave in a black Mercedes Benz car. Other delegation members left the hotel in a white minibus.

The reports indicate that planning for the historic summit, initially scheduled for June 12, is moving ahead after Trump called it off last week. A day later, Trump said he had reconsidered, and officials from both countries were meeting to work out details.

When Kim Chang Son was asked by a reporter at the Beijing airport if he was flying to Singapore for talks with the United States (US), he said he was "going there to play," according to footage from Nippon Television Network.

Meanwhile, North Korea's Kim Yong Chol, a senior official dealing with inter-Korean affairs, was scheduled to fly to the US on Wednesday after speaking to Chinese officials in Beijing, South Korea's Yonhap news agency said, citing an unnamed source.

Due to sanctions against him, Kim Yong Chol is banned from visiting the US normally. His visit to the US would indicate a waiver was granted.

The US and South Korea blacklisted Kim Yong Chol for supporting the North's nuclear and missile programmes in 2010 and 2016, respectively.

Yonhap added Choe Kang Il, a North Korean foreign ministry official involved with North America issues, was also spotted at Beijing Capital International Airport. Yonhap did not say whether Choe would be accompanying Kim Yong Chol.

In a flurry of diplomacy over the weekend, Kim Jong Un and South Korean President Moon Jae In held a surprise meeting on Saturday at the border village of Panmunjom, during which they agreed the North Korea-US summit must be held.

And on Sunday, the US State Department said American and North Korean officials had met at Panmunjom. Sung Kim, the former US ambassador to South Korea and current ambassador to the Philippines, led that American delegation, an American official told Reuters.

Moon said on Monday there could be more impromptu talks between the two Koreas in the lead-up to the summit.

In Kim and Moon's first, upbeat meeting on April 27, they agreed to seek the "complete denuclearisation" of the Korean peninsula - but didn't define what that meant, or how that would proceed.

Since then, North Korea has rejected US demands for it to unilaterally abandon its nuclear weapons programme that experts say could threaten the US.

Pyongyang also demanded the US halt future joint military drills with South Korea if it truly wishes for talks with North Korea, the North's Rodong Sinmun said on Tuesday. In response to reporters' questions regarding the report, South Korea's defence ministry said it does not have plans to change joint exercise schedules with the US military.

Analysts believe Washington is trying to determine whether North Korea is willing to agree on sufficient steps towards denuclearisation to allow a summit to take place.

North Korea defends its nuclear and missile programmes as a deterrent against perceived aggression by the US, which keeps 28,500 troops in South Korea, a legacy of the 1950-53 Korean War, which ended in a truce, not a peace treaty.

It has long said it is open to eventually giving up its nuclear arsenal if the US withdraws its troops from South Korea and ends its "nuclear umbrella" alliance with Seoul.