North Korean state media on Wednesday made no mention of new appearances by leader Kim Jong Un, amid continued international speculation over his health following reports he underwent surgery.

Officials in South Korea and China and sources familiar with US intelligence have cast doubt on media reports that claimed Kim was gravely ill after a cardiovascular procedure, while the White House said it was closely monitoring the issue.

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US President Donald Trump, who held unprecedented summits with Kim in 2018 and 2019 in an attempt to persuade him to give up his nuclear weapons, said the South Korean and US reports had not been confirmed and he did not put much credence in them.

"I just hope he's doing fine," Trump told a White House news conference on Tuesday. "I've had a very good relationship with Kim Jong Un. And I'd like to see him do well. We'll see how he does. We don't know if the reports are true."

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

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

Mulberry picking, no Kim

On Wednesday, the main headlines from the official Korean Central News Agency (KCNA) included pieces on sports equipment, mulberry picking and a meeting in Bangladesh to study North Korea's "juche" or self-reliance ideology. The official Rodong Sinmun newspaper carried articles on a self-sufficient economy and anti-coronavirus measures.

There was no mention of Kim's whereabouts.

North Korean leader Kim Jong Un guides a drill of mortar sub-units of North Korean Army in this image released by North Korea's Korean Central News Agency on April 10, 2020 [KCNA/via Reuters]

Daily NK, a Seoul-based website, reported late on Monday that Kim, who is believed to be about 36, was hospitalised on April 12, hours before the cardiovascular procedure.

It said his health had deteriorated since August due to heavy smoking, obesity and overwork.

Citing one unnamed North Korean source it said Kim was now receiving treatment at a villa in the Mount Myohyang resort north of the capital Pyongyang.

On Tuesday, media broadcaster CNN reported an unnamed US official saying that Washington was "monitoring intelligence" that Kim was in "grave danger" after surgery.

However, two South Korean government officials rejected the CNN claims. China, North Korea's only main ally, also dismissed the reports.

South Korea's presidential Blue House 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 has not been any unusual movement or emergency reaction from North Korea's governing party, military or cabinet.

According to KCNA, Kim 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. State media have since reported he sent greetings to Syrian President Bashar al-Assad and Cuban President Miguel Díaz-Canel as well as arranging special birthday meals for two North Korean officials and a new centenarian.

Kim Yo Jong helps her brother sign a joint statement following the summit with South Korean President Moon Jae-in at the Paekhwawon State Guesthouse in Pyongyang, North Korea, on September 19, 2018 [File: Pyongyang Press Corps Pool via AP]

Kim's absence from state media often triggers speculation.

Succession issues

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 had a cyst removed from his ankle.

Governments and media outside North Korea have a mixed record on tracking developments among its 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 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 a new senior post.

It is unclear what would happen if Kim were sidelined by health problems or died.

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

"The basic assumption would be maybe it would be someone in the family," said National Security Advisor Robert O'Brien in a comment made to Fox News channel. "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."

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.

However, Koh Yu-hwan, a North Korea expert at Seoul's Dongguk University and a policy adviser to South Korean President Moon Jae-in, sees the possibility of a violent power struggle.

While his sister would most likely emerge as leader during a transitional period, other members of the top elite could try to reduce her to a figurehead while making important decisions from the shadows, Koh said.

The fact that North Korea is an extremely patriarchal society has led some to wonder if Kim Yo Jong would only serve as a temporary figurehead and then be replaced by a collective leadership similar to ones established after the deaths of other communist dictators.

"North Korean politics and the three hereditary power transfers have been male-centered. I wonder whether she can really overcome bloody socialist power struggles and exercise her power," said Nam Sung-wook, a professor at Korea University in South Korea.

A collective leadership would likely be headed by Choe Ryong Hae, North Korea's ceremonial head of state who officially ranks No 2 in the country's current power hierarchy, Nam said.

But Choe is still not a Kim family member, and that could raise questions about his legitimacy and put North Korea into deeper political chaos, according to other observers.

Other Kim family members who might take over include Kim Pyong Il, the 65-year-old half-brother of Kim Jong Il who reportedly returned home in November after decades in Europe as a diplomat.

Kim Pyong Il's age "could make him a reasonable front man for collective leadership by the State Affairs Commission and regent for the preferred next generation successor", said Leif-Eric Easley, a professor at Ewha University in Seoul.

"However, elite power dynamics and danger of instability might make this an unlikely option."