On Saturday, a USA -based North Korea monitoring project, 38 North, said satellite images showed what was believed to be Kim's personal train parked at a station reserved for his use in Wonsan on April 21 and 23.
North Korea is notoriously reclusive, and while they have not confirmed any cases of coronavirus, it is believed the disease is rife there.
The report comes amid media speculation that Jong-un might be seriously ill.
South Korean Unification Minister Kim Yeon-chul suggested Kim Jong-un made a decision to skip the anniversary celebration of his grandfather's birth because of the coronavirus pandemic, but since the regime does not want to admit it has a pandemic, the dictator chose to disappear without explanation.
First seen in public during the funeral of late leader Kim Jong-il in 2011, Kim Yo-jong's public profile has been quite visible in the past two years. The episode has underscored concerns about instability in the secretive, impoverished and nuclear-armed state because Kim has named no clear successor since taking power after his own father's death eight years ago.
"It's one of his favorite homes", said Michael Madden, a North Korean management expert at the US -based Stimson Center, adding that Kim would own about 13 large complexes across the country.
The area saw a burst of military activity on April 14, including cruise missile tests and fighter jet manoeuvres. "We're watching it closely", Mr Pompeo told Fox News.
North Korea is prone to food shortages, with as many as 1.1 million people dying of starvation and related diseases during the famines of the 1990s, according to South Korean estimates. Leadership in North Korea has operated as a quasi-monarchy ever since Kim Il Sung took power.
However, South Korean officials have contradicted this theory, pointing out that numerous public events in North Korea have been canceled due to the outbreak of coronavirus.
Despite the widespread buzz around Jong-un's younger sister Kim Yo-jong, the truth remains that patriarchal and conservative society and male-dominated politics in North Korea would not allow a woman to assume the role of the supreme leader.
The Post claimed the regime in Pyongyang professed itself "bewildered" by these efforts to spread false news about Kim's death and ominously vowed to find those responsible, a threat disturbing enough to reduce global telephone calls, text messages, and Internet traffic from North Koreans. "The problem is that a Kim Yo Jong-led North Korea is unlikely to be sustainable", he told Bloomberg. "Kim Yo Jong has a special status in the regime, and I think in this case, her connection to the Kim family trumps her gender".
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