TOKYO — Indications that North Korean leader Kim Jong Un is still alive and in the coastal resort of Wonsan are mounting, as satellite images showed his train apparently traveled there in the past few days, and U.S. and South Korean officials said they did not believe he had died.

Rumors of Kim’s possible demise have been swirling since he skipped celebrations for his grandfather’s birthday on April 15 and after a South Korea media report said he had undergone a cardiovascular procedure on April 12 in a hospital outside Pyongyang and was recuperating in a nearby villa.

But U.S. and South Korean intelligence services remain skeptical of reports that Kim is dead or gravely ill, according to three government officials familiar with the matter.

“We understand that Chairman Kim Jong Un has been in Wonsan this week,” said a South Korean official who spoke on the condition of anonymity to discuss sensitive intelligence matters.

Another official said that Kim’s health is among the North’s most closely guarded secrets, but noted that neither government has evidence of his death.

Commercial satellite images published by the 38 North website, affiliated with the Stimson Center, showed what appeared to be Kim’s 250-meter-long personal train at a railway station dedicated to the Kim family in Wonsan on April 21 and 23.

The train was not present on April 15.

“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,” Martyn Williams, Peter Makowsky and Jenny Town wrote in their report.

To be sure, something strange is going down in the intensely secretive state.

Thae Yong-ho, a former senior North Korean diplomat who defected to the South in 2016, said in a statement it was “unprecedented” that Kim did not appear to lay a wreath at the Kumsusan Palace of the Sun, where his grandfather and father’s bodies are both embalmed.

But the fact that Kim has not been seen in public for two weeks is not in itself unusual — it falls within the “normal range” of absence for the North Korean leader, said Rachel Minyoung Lee, a former North Korea open-source intelligence analyst for the U.S. government.

Indeed, Kim disappeared from public view for three weeks between a Lunar New Year concert on Jan. 25 and a February event at the Kumsusan Palace of the Sun to mark his father’s birthday. He was not seen in public for another 13 days before offering “guidance” for military training on Feb. 28, according to state media reports.

“His absence from the Kumsusan Palace on Kim Il Sung’s birthday was unusual, but that alone is not evidence enough to say Kim Jong Un is in trouble,” Lee said.

She added that North Korea’s silence since then should not be over-interpreted. “North Korea does not react to rumors about the leader’s health,” she said.

The Daily NK website first reported that Kim had undergone an operation on April 12 at a hospital near Mount Myohyang and was recuperating at a nearby villa.

But if Kim were gravely ill, it’s unlikely he would have left the hospital and traveled by train to Wonsan, a distance of over 150 miles. And if he had died and officials wanted to maintain secrecy, it’s unlikely his body would have been transported across the country.

Speculation intensified last week when CNN reported an unnamed U.S. official had said Washington was monitoring intelligence suggesting Kim was in “grave danger” after surgery. But officials in Seoul and Washington soon downplayed or contradicted that report.

On Saturday, Reuters reported that China had dispatched a team including medical experts “to advise on” Kim. The news agency cited three unnamed sources but cautioned that it was “unable to immediately determine what the trip by the Chinese team signaled in terms of Kim’s health.”

A Japanese magazine cited a single unnamed Chinese medical source as saying Kim was in a “vegetative state” after an operation went wrong. A Hong Kong TV executive posted on social media that Kim was dead.

Kim is overweight and is frequently seen smoking; it would hardly be a surprise if he had heart problems. But the movement of the train and other indications he is in Wonsan appear to contradict the notion he is at death’s door.

Dong-a Ilbo, a South Korean newspaper, cited a U.S. official in Washington saying Kim had been seen walking around in Wonsan.

For experienced North Korea watchers, this territory is not unfamiliar. Kim’s father, Kim Jong Il, and grandfather, Kim Il Song, were both subject to many false death reports. Kim Jong Un has gone into seclusion and missed important public events before, only to reemerge, noted Bruce Klingner, a former U.S. intelligence official who now works at the Heritage Foundation.

“On the other hand, the first that the U.S. intelligence community and even North Korean ministries knew of Kim Jong Il’s death in 2011 was the official announcement two days later,” Klingner noted.

When Kim Jong Il had a stroke in 2008, Thae said, colleagues at the Foreign Ministry knew nothing for an entire week, even as official documents that required the leader’s approval piled up.

But it’s also noteworthy that French doctors attended to the North Korean leader on that occasion, analysts say, and it’s far from clear North Koreans would invite in Chinese officials and doctors — and possible Chinese interference — if there really were a succession crisis playing out behind the scenes.

North Korea’s relationship with China is based more on overlapping interests than any real trust.

Indeed, analysts, officials and diplomats say concerns about the novel coronavirus represent another plausible theory to explain Kim’s vanishing act, especially if a senior official had contracted the virus or come into contact with someone who had.

The regime has repeatedly underlined its deep concern about a possible outbreak of the coronavirus and completely shut its borders early in the global crisis.

A World Health Organization official told Voice of America this past week that 740 people in North Korea had been tested for the novel coronavirus by April 17, and none was found to be infected.

But many health analysts are skeptical, and Radio Free Asia reported that officials admitted the virus had spread through the country when talking with local organizations and neighborhood watch units.

The Tokyo Shimbun newspaper reported that Kim appears to be undergoing “voluntary isolation” in Wonsan, citing a high-ranking Japanese government official, and quoted North Korean sources as saying he had gone there after one of his bodyguards was found to have the virus. That’s not the sort of thing North Korea would admit publicly, especially given its insistence it has no cases of the virus.

There have been no new photographs of Kim on North Korea state media for two weeks, but that’s not necessarily a sign that anything is amiss.

Kim sent messages last week to Syrian President Bashar al-Assad and Cuban President Miguel Díaz-Canel, the state Korean Central News Agency reported, and sent a letter thanking construction workers for building the city of Samjiyon, the official Rodong Sinmun newspaper reported on Sunday.

“Experienced Korea watchers are counseling ‘we don’t know, we have to wait for confirmation, so have another drink,’ ” Klingner said, “while those new to North Korea are taking the rumors at face value and panicking about loss of control of nuclear weapons.”

Hudson reported from Washington and Min Joo Kim from Seoul.