South Korean officials reported no unusual activity in North Korea on Tuesday following unconfirmed media reports Monday night that leader Kim Jong Un was in fragile health after surgery.

South Korea's presidential office said Kim appeared to be handling state affairs as usual and that it had no information about rumors regarding his health. But many will be watching closely for any signs of trouble in North Korea, and whether it will address the reports — something it has not yet done.

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On Monday, the United States reportedly received intelligence that North Korean dictator Kim Jong Un may be in "grave danger after surgery," according to a report first published Monday night by CNN, citing an official with direct knowledge of the matter. There were very few other details.

Speculation often surfaces about North Korea's leadership based on attendance at important state events.

Kim, who is in his mid-30s, missed the celebration of the birthday of his late grandfather and state founder Kim Il Sung on April 15, the country's most important holiday.

But he presided over a meeting on April 11, discussing coronavirus prevention and electing his sister as an alternate member of the political bureau of the ruling Workers' Party, according to the North's official Korean Central News Agency. And state media have since reported he sent greetings to Syrian President Bashar Assad and Cuban President Miguel Díaz-Canel as well as "birthday spreads" to two North Korean officials and a new centenarian.

The White House has so far declined to comment about the report, and there was no other immediate confirmation.

The United States and North Korea appeared to be barreling toward war in 2017, with the countries trading insults and threats of destruction. The next two years saw a surprising series of summits, including three between Kim and Trump, as Kim pursued diplomacy in hopes of ending crippling economic sanctions and obtaining security guarantees. But through it all he maintained his right to a nuclear arsenal, and most diplomacy has stalemated since.

It's unclear what would happen if Kim is sidelined by health problems or dies.

Cheong Seong-Chang, an analyst at the private Sejong Institute in South Korea, said political upheaval would be unlikely as Kim's sister, Kim Yo Jong, is already exercising significant influence within the government, and most members of North Korea's leadership share an interest with the Kim family in maintaining the North's system.

While North Korea has not made clear who would potentially succeed Kim, some experts believe Kim Yo Jong would step in as leader, at least during a transitional period. Others believe North Korea could be ruled by collective leadership of ruling party elites, similar to the post-Stalin Soviet Union.

"We have no information to confirm regarding rumors about Chairman Kim Jong Un's health issue that have been reported by some media outlets," South Korean presidential spokesman Kang Min-seok said. "Also, no unusual developments have been detected inside North Korea."

The presidential office later said Kim is believed to be staying at an unspecified location outside of Pyongyang, North Korea's capital, with some close confidants. It said Kim appeared to be normally engaged with state affairs and there wasn't any unusual movement or emergency reaction from North Korea's ruling party, military or Cabinet.

A U.S. official said the White House was aware before the reports appeared late Monday that Kim's health might be precarious. The official said the U.S. had information that Kim may have undergone surgery and that complications may have rendered him "incapacitated or worse." But, the official stressed that the U.S. had nothing to confirm the surgery had taken place or that any complications had occurred.

The U.S. official, who was not authorized to discuss the matter publicly and spoke on condition of anonymity, would not elaborate on where the information came from or when it had been received. The White House and State Department had no comment.

Conservative South Korean lawmaker Yoon Sang-hyun, chairman of the National Assembly's foreign affairs and unification committee, said he was told by unspecified non-government sources that Kim had surgery for cardiovascular problems. But an official from Seoul's National Intelligence Service, who didn't want to be named, citing office rules, said the spy agency couldn't confirm whether Kim had surgery.

Kim In-chul, spokesman for South Korea's Foreign Ministry, said Seoul and Washington are maintaining close communication but didn't provide a direct answer when asked whether the allies exchanged any meaningful intelligence about Kim's health.

Outside governments and media have a mixed record on tracking developments among North Korea's ruling elite, made difficult by the North's stringent control of information about them.

In 2016, South Korean media quoted intelligence officials as saying Kim Jong Un had had a former military chief executed for corruption and other charges. But months later, North Korea's state media showed Ri Yong Gil alive and serving in new senior posts.

Kim's absence from state media often triggers speculation. In 2014, he vanished from the public eye for nearly six weeks before reappearing with a cane. South Korea's spy agency said days later that he had a cyst removed from his ankle.

Kim, believed to be 36, took power upon his father's death in December 2011 and is the third generation of his family to rule the country.

Kim not being there raised suspicions about his health, although experts can’t say for certain if that’s actually the case because North Korea’s oppressive regime typically suppresses any information about Kim.

The CNN report also emphasized the leader’s absence from state events in the past has led to speculation but nothing more.

“There have been a number of recent rumors about Kim’s health (smoking, heart and brain). If Kim is hospitalized, it would explain why he wasn’t present on the important April 15 celebrations,” said Bruce Klingner, a senior research fellow at the Heritage Foundation and former CIA deputy division chief for North Korea, according to CNN. “But, over the years, there have been a number of false health rumors about Kim Jong Un or his father. We’ll have to wait and see.”

In 2014 Kim was not seen in public for more than a month only to reemerge after a reported surgery on his ankle.

“It’s easy to be wrong on this one,” said John Delury, a professor of international relations at Yonsei University in Seoul.

Kim was reportedly last seen at a government meeting on North Korean state media on April 11.

Kim Il Sung was the founder of North Korea, which he ruled from the country’s establishment in 1948 until his death in 1994.

The Associated Press contributed to this report.