North Korean leader Kim Jong Un hasn't been publicly seen in 2 weeks, fueling reports and rumors that he may be dead or in grave condition. Here's what we know.

• Speculation mounted on Saturday that North Korean leader Kim Jong Un may be dead or in grave condition after a surgery.
• The rumors started after Kim did not appear at a celebration for one of the country's most celebrated holidays on April 15: the birthday of founder Kim Il Sung.
• The accuracy of these reports remains unclear — the South Korean and Chinese governments have downplayed concerns, and United States intelligence has not yet confirmed anything.
• Experts have previously noted that Kim Jong Un had certain health risks and could suffer cardiac issues due to his weight.
• The rumors have sparked a flurry of questions about Kim Jong Un's line of succession, and who might take his place if he dies.
• Visit Business Insider's homepage for more stories.

Speculation mounted on Saturday over North Korean leader Kim Jong Un's health as he hasn't been seen in public since April 11 when he presided over a party meeting.

It's fueled reports from multiple outlets citing sources in China and Japan that Kim, who is believed to be 36, is in grave condition after a cardiovascular surgery, or may even be dead.

The accuracy of these reports is unclear. The South Korean government, which monitors North Korea closely, downplayed the rumors on April 21 and said Kim appears to still be running the country. 

"No unusual developments have been detected inside North Korea," South Korean presidential spokesman Kang Min Seok said.

Chinese officials have also downplayed rumors that Kim is critically ill. US intelligence is reportedly monitoring the situation, but President Trump said earlier this week the US had no reliable information regarding Kim's health. 

The speculation over his health has also prompted questions over who might take over as North Korea's leader if Kim dies. He has a complicated family tree, and his three rumored children are too young to lead, but his sister, Kim Yo Jong, is considered to be a powerful figure who could run the country in the meantime.

How the rumors began, and how they've evolved since

The rumors about Kim's health first began on April 15, when he did not appear at a celebration commemorating the birth of Kim Il Sung, his grandfather and the founder of North Korea. The birthday is the country's most important holiday.

Then, the rumors intensified when a South Korean news outlet published a story reporting the North Korean leader had undergone heart surgery and was recovering at a villa outside Pyongyang, the nation's capital. The report relied on a single unnamed source inside North Korea.

Reuters reported on Friday that China dispatched a team of medical experts to travel to North Korea and advise on Kim's health, citing three sources. But the outlet was quick to note it wasn't able to determine what the development meant about the North Korean leader's health, and the Chinese government did not respond to Reuters' requests for comment.

Adding to the mystery were satellite images published  Saturday by a Washington-based North Korea monitoring project, 38 North. The images showed what appeared to be Kim Jong Un's private train at a resort town in North Korea.

The information about the train remains unconfirmed, and it's unclear Kim himself was on the train. 

"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," 38 North said.

As with most news regarding the hermit kingdom, the reports are near-impossible to verify. The government tightly controls its media apparatus, and has refused to release even the most basic information about the Kim family — including Kim Jong Un's age, the existence of his children, and when he married his wife.

Kim Jong Un is at risk from obesity and cardiac health issues, experts say

Media outlets in North Korea, including the state-run Korean Central News Agency, have been silent so far about Kim's absence from public events. 

North Korea watchers say that one of Kim's biggest risk factors was his poor health, particularly risks from cardiac issues due to his weight, per The Washington Post's Anna Fifield.

"The young leader looks like a heart attack waiting to happen and has clearly had problems," Fifield wrote in her book, "The Great Successor."

Fifield also noted that the North Korean leader is a heavy smoker.

North Korean leaders have previously disappeared only to reappear at public events weeks later

Back in 2014, the North Korean leader disappeared for nearly five weeks, fueling rumors he suffered from gout, a severe hangover, or had been overthrown in a coup.

North Korean state TV later showed Kim walking with a cane, and announced the leader wasn't "feeling well."

The same happened for the country's previous leader, Kim Jong Il. In 2008, he was publicly absent for several months. It was later confirmed he suffered a stroke, The New York Times reported.

Information around significant events in the country can take several days or weeks to make its way to the outside world. When Kim Jong Il died in 2011, it took time for intelligence agencies to confirm it — but only after the news was announced on state television two days later.

Both Kim's father and grandfather died of heart failure.

SEE ALSO: What we know about Kim Jong Un's 3 possible heirs

DON'T MISS: Meet North Korea's most powerful woman, Kim Yo Jong: Kim Jong Un's 30-something sister who could lead the country if something happens to him since his heirs are too young

Join the conversation about this story »

NOW WATCH: Why thoroughbred horse semen is the world's most expensive liquid