South Korean and Chinese officials on Tuesday cast doubt on reports that North Korean leader Kim Jong Un is ill after media outlets said he had undergone a cardiovascular procedure and was in “grave danger,” while U.S. officials said they were closely monitoring the situation.

Daily NK, a Seoul-based speciality website, reported late on Monday, citing one unnamed source in North Korea, that Kim was recovering after undergoing the procedure on April 12. The North Korean leader is believed to be about 36.

Two South Korean government officials rejected an earlier CNN report citing an unnamed U.S. official saying the United States was “monitoring intelligence” that Kim was in grave danger after surgery but they did not elaborate on whether Kim had undergone surgery. South Korea’s presidential Blue House said there were no unusual signs coming from North Korea.

Bloomberg News separately quoted an unnamed U.S. official as saying the White House was told that Kim had taken a turn for the worse after the surgery.

“We’re monitoring these reports very closely,” U.S. President Donald Trump’s national security adviser, Robert O’Brien, told Fox News in an interview on Tuesday.

Asked about how any political succession would work in North Korea, O’Brien said, “The basic assumption would be maybe it would be someone in the family. But, again, it’s too early to talk about that because we just don’t know what condition Chairman Kim is in and we’ll have to see how it plays out.”

Kim is a third-generation hereditary leader who rules reclusive, nuclear-armed North Korea with an iron fist, holding the titles of head of state and commander in chief of the military since late 2011.

In recent years Kim has launched a diplomatic offensive to promote himself and his country as a world leader, holding three meetings with Trump, four with South Korean President Moon Jae-in and five with Chinese President Xi Jinping.

Trump has described Kim as a friend but the unprecedented engagement by a U.S. president with a North Korean leader has failed to slow Kim’s nuclear weapons program, which now poses a threat to the United States.

Kim is the unquestioned leader of North Korea and the sole commander of its nuclear arsenal. He has no clear successor and any instability in the country could present a major international risk.

North Korea’s official KCNA news agency gave no indication of the whereabouts of Kim in routine dispatches on Tuesday, but said he had sent birthday gifts to prominent citizens.

Speaking to Reuters, an official at the Chinese Communist Party’s International Liaison Department, which deals with North Korea, expressed the belief that Kim was not critically ill. China is North Korea’s only major ally.

Chinese foreign ministry spokesman Geng Shuang said Beijing was aware of reports about Kim’s health, but said it does not know their source, without commenting on whether it has any information about the situation.

Daily NK said Kim had been hospitalized on April 12, just hours before the cardiovascular procedure, as his health had deteriorated since August due to heavy smoking, obesity and overwork. It said he was now receiving treatment at a villa in the Mount Myohyang resort north of the capital Pyongyang.

“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 took two well-publicized rides on a stallion on the snowy slopes of the mountain in October and December.

Speculation about Kim’s health first arose due to his absence from the anniversary of the birthday of its founding father and Kim’s grandfather, Kim Il Sung, on April 15.

KIM’S HEALTH KEY TO STABILITY

Authoritative U.S. sources familiar with internal U.S. government reporting on North Korea questioned the CNN report that Kim was in “grave danger.”

“Any credible direct reporting having to do with Kim would be highly compartmented intelligence and unlikely to leak to the media,” a Korea specialist working for the U.S. government said on condition of anonymity.

Reporting from inside North Korea is notoriously difficult, especially on matters concerning the country’s leadership, given tight controls on information. There have been false and conflicting reports in the past on matters related to its leaders.

Kim’s potential health issues could fuel uncertainty over the future of North Korea’s dynastic rule and stalled denuclearisation talks with the United States.

With no details known about his young children, analysts said his sister and loyalists could form a regency until a successor is old enough to take over.

Kim was the first North Korean leader to cross the border into South Korea to meet Moon in 2018. Both Koreas are technically still at war, as the Korean War of 1950-1953 ended in an armistice, not a peace treaty.

Kim has sought to have international sanctions against his country eased, but has refused to dismantle his nuclear weapons program.