North Korean leader, Kim Jong Un, is said to be in grave health danger after a cardiovascular surgery, according to multiple U.S. media reports.

The reports quoted intelligence sources.

However, Reuters, quoting a South Korean medium, reported that the 36 year-old Supreme leader is receiving treatment after undergoing the surgery early this month.

Speculations developed over Kim’s health following his absence from a key anniversary event.

North Korea marked the anniversary of the birthday of its founding father and Kim’s grandfather, Kim Il Sung, as a national holiday on April 15, but Kim was not seen in attendance.

Daily NK, a speciality website run mostly by North Korean defectors, cited unidentified sources inside the isolated state saying Kim is recovering at a villa in the Mount Kumgang resort county of Hyangsan on the east coast after getting the procedure on April 12 at a hospital there.

Reporting from inside North Korea is notoriously difficult, especially on matters concerning the country’s leadership, given tight controls on information.

South Korea’s Unification Ministry, which handles inter-Korean affairs, declined to comment on the report.

Kim’s health has deteriorated in recent months due to heavy smoking, obesity and overwork, the Daily NK report said.

“My understanding is that he had been struggling (with cardiovascular problems) since last August but it worsened after repeated visits to Mount Paektu,” a source was quoted as saying, referring to the country’s sacred mountain.

Kim left for the hospital after presiding over a meeting of the ruling Workers’ Party’s politburo on April 11, where Kim was publicly last seen, the report said.

Pyongyang fired multiple short-range missiles last week which Seoul officials said were also part of the Kim Il Sung birthday celebration. Such military events would usually be observed by Kim, but there was no KCNA report on the test at all.