Absent from important national events, North Korean dictator Kim Jong Un is believed to be undergoing medical treatment by a team of doctors from China which has limited his public appearances, according to reports, which are being closely monitored by the White House.

Reuters quoted “three people familiar with the situation” as saying that a delegation led by a senior member of the Chinese Communist Party’s International Liaison Department left Beijing for North Korea Thursday and the delegation includes medical experts to advise on Kim’s health.

A Seoul-based website, Daily NK, reported that Kim underwent a cardiovascular procedure on April 12, and was recovering. According to North Korea’s state media, Kim made a public appearance on April 11. However, there were no reports about his appearance on the birth anniversary of his grandfather, Kim Il Sung, on April 15, although it’s an important occasion in North Korea.

Kim is known to have a family history of cardiovascular problems, he is a heavy smoker and has gained weight since he took power in 2011.

National security adviser Robert O’Brien acknowledged reports about Kim’s health and that the Trump administration is trying to learn more, according to The Wall Street Journal.

“We’re monitoring these reports very closely,” O’Brien was quoted as saying on Fox News. “They’re parsimonious with the information that they provide about many things, including the health of Kim Jong Un, so we’re monitoring those developments closely.”

Earlier during the week, U.S. intelligence officials looked into reports that that suggested Kim’s condition might be grave, a U.S. official told The Wall Street Journal, adding that the situation remained fluid.

However, a spokesman for Seoul’s presidential Blue House was quoted as saying that they saw no “extraordinary developments inside North Korea.”

“The main concern would be if a sudden death without an heir leads to an internal crisis that then prompts China, Russia, the U.S., and South Korea to act,” Duyeon Kim, a senior adviser for the Brussels-based International Crisis Group, an independent non-profit, was quoted as saying. “But we need to be very careful with rumors and thinly sourced reports because we’ve been wrong many times before.”

North Korea is believed to be the world’s most secretive regime.

Kim is the third son of former North Korean Supreme Leader Kim Jong Il and grandson of Kim Il Sung, who served as North Korea’s dictator since its founding in 1948 until his death in 1994.

According to Heavy.com, much of Kim’s early life is unknown, including his actual date of birth. According to North Korea, Kim was born on Jan. 8, 1982. However, South Korean records indicate that his birth came on Jan. 8, 1983.

Kim and his wife, Ri Sol Ju, are believed to have a daughter named Kim Ju Ae although she has never been seen in public or photographed.

National Basketball Association legend and Kim’s friend Dennis Rodman, who travels to North Korea every so often to hang out with Kim, has confirmed the existence of Kim’s daughter and even revealed her name in an interview with The Guardian in 2013.

“I held their baby Ju Ae and spoke with Ms. Ri as well,” Rodman said in describing a trip to Pyongyang he had recently taken. “He’s a good dad and has a beautiful family. Kim told me, ‘I’ll see you in December.’”