The Korean Central Broadcasting Station also carried a similar report.

The reports came amid lingering speculation that something might be wrong with Kim's health since he missed an important annual ceremony on April 15 commemorating the birthday of late state founder and his grandfather, Kim Il-sung.

Some unconfirmed media reports have speculated that Kim could be "in grave danger" after surgery. ALSO READ: North Korean media silent on Kim Jong-Un as speculation on health grows

But South Korean officials have dismissed such speculation as untrue, saying nothing unusual was going on in the North and Kim Jong-un was believed to be staying in the Wonsan region.

Corroborating the intelligence was a report by the US monitoring website 38 North that satellite imagery showed what appeared to be Kim Jong-un's special train parked at a station in "his Wonsan compound since at least April 21".

"The train's presence does not prove the whereabouts of the North Korean leader or indicate anything about his health, but it does lend weight to reports that Kim is staying at an elite area on the country's eastern coast," it added.

Moon Chung-in, a special security adviser to South Korean President Moon Jae-in, also said Sunday in an interview with Fox News that Kim Jong-un was "alive and well", reports Yonhap News Agency.

On Monday, South Korea's Unification Ministry on Monday reaffirmed no unusual signs have been detected in the North. ALSO READ: Satellite photos find train likely belonging to Kim outside Pyongyang

"We have nothing to confirm in regards to speculation over leader Kim Jong-un's health. However, our stance that there is no unusual activity currently in North Korea, as announced by the National Security Council, is still in effect to this point," Cho Hey-sil, the Ministry's deputy spokesperson, told the media.

The Wonsan-Kalma tourist zone is one of Kim Jong-un's key pet construction projects.

The leader, who sent a similar thank-you message to the workers in February, has sought to develop the North's tourism in an effort to beef up an economy faltering under international sanctions.

Kim Jong-un was last seen in state media on April 11 presiding over a political bureau meeting of the ruling Workers' Party, calling for strict measures against the coronavirus. ALSO READ: Trump rejects reports of Kim Jong-un's illness, says 'hope he's doing fine'

But his absence from a key ceremony commemorating the 108th birth anniversary of Kim Il-sung on April 15 has sparked speculation over his health. He has never skipped his trip to the mausoleum since taking office in late 2011.

North Korean state media have recently put out reports on Kim sending diplomatic letters and conveying gifts to honoured citizens.

But no reports on the leader's "field guidance" trips or photos on his public activities have been released by state media for more than two weeks.