Amid rising rumors about the health of North Korea's leader, Kim Jong-un, the Korean Central News Agency said on Sunday that Kim expressed his "appreciation" for the workers who are building a facility in the northern border region "Samgyeon".

North Korean radio also released a similar report today, saying that Kim thanked the workers, who are sincerely contributing to the construction of a power plant. Active construction and development works are underway in Samgyeon County, near Mount Baekdu, which symbolizes the North Korean founding family.

However, North Korean media reports did not mention Kim Jong Un's whereabouts or health condition.

This comes as satellite imagery detected a train likely to be North Korean leader Kim Jong-un in a resort in eastern North Korea, according to the American website «38 Northrath», at a time when Kim raises speculation.

Satellite imagery, according to the site, showed "a train of approximately 250 meters" parked at the driving railway station at a complex owned by Kim in Wonsan, "since April 21 at least."

The train appears in the pictures on April 21 and 23 at the station designated for the Kim family, according to a website specializing in tracking North Korean news in an article published on Saturday.

38 North explains that the presence of the train in that area "does not prove anything about the location of the North Korean leader nor does it confirm anything about his health."

"But that gives credibility to the information that Kim is located in an area designated for the elite on the east coast," he added.

Kim appeared for the last time on April 11 during a meeting of the party's political bureau, then on an inspection tour of an air base, which was reported by official media on April 12.

The "Daily in Kai" website, which is run by defected North Koreans, said that in April, the North Korean leader underwent surgery because of suffering from problems in the arteries of the heart, and that he was going through a recovery period in Pune Gan province in the north.

Quoting an unidentified North Korean source, the website said that the 36-year-old Kim had been emergency treated for problems related to "his heavy smoking, obesity and fatigue."

South Korea, still practically at war with North Korea, played down the importance of that news.

CNN also quoted a US official as saying that Washington was "studying information" stating that Kim Jong-un was "in a very serious condition as a result of surgery."

On Thursday, however, US President Donald Trump considered that information related to Kim's deteriorating health was probably "wrong".

The South Korean "SBS" channel Thursday quoted a government official as saying that Kim had probably been in Wonsan for at least four days, and that he would appear publicly soon.

The channel added that the South Korean army is watching the stop of the Kim train, which was seen in Wonsan, while its plane, which it usually uses to move to Wonsan, is still in Pyongyang.

This is not the first time that Kim's "absence" has cast doubt.

In 2014, Kim did not appear publicly for six weeks before seeing him again leaning against a stick.

At the time, South Korean intelligence confirmed, according to Yonhap, that the North Korean president had undergone an ankle removal.

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