North Korean media presented a business-as-usual image, carrying routine reporting of Kim's achievements and publishing some of his older, or undated, comments on issues like the economy.

South Korean and Chinese officials and sources familiar with U.S. intelligence have cast doubt on South Korean and U.S. media reports that he was seriously sick, while the White House said it was closely monitoring the matter.

However, on Wednesday one U.S. government source who had previously played down reports that Kim was seriously ill said it was a possibility that was now being looked at closely.

U.S. 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 on Tuesday the reports had not been confirmed and he did not put much credence in them.

"We'll see how he does," Trump told a White House news conference. "We don't know if the reports are true."

U.S. Secretary of State Mike Pompeo said on Wednesday he had nothing to add to Trump's remarks. "I think it was, we're watching closely what's taking place there," Pompeo told a news conference.

The second-highest ranking U.S. general said he had no intelligence to "confirm or deny" reports about Kim's health and he assumed he was still in control of North Korea's military.

"I have no reason not to assume that," Air Force General John Hyten, vice chairman of the Joint Chiefs of Staff, told a news conference.

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.

Kim is a third-generation hereditary leader who rules North Korea with an iron fist, coming to power after his father, Kim Jong Il, died in 2011 from a heart attack.

Reporting from inside North Korea is notoriously difficult, especially on matters concerning its leadership, given tight controls on information. There have been past false reports regarding its leaders, but the fact Kim has no clear successor means any instability in the nuclear-armed country could present a major international risk.

On Wednesday, the main headlines from North Korea's state 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 older or undated remarks attributed to Kim in articles about the economy, the textile industry, city development, and other topics.

As usual Kim's name was plastered all over the newspaper. But there were no reports on his whereabouts.

Official media has however continued to report the sending of routine diplomatic letters by Kim, and KCNA said he sent a reply on Wednesday to Syrian President Bashar al-Assad, thanking him for a message to mark the birthday of the North Korean leader's grandfather, Kim Il Sung.

South Korea's presidential Blue House said it could not confirm Kim's whereabouts, or whether he had undergone surgery. It said South Korea had detected no unusual activity in North Korea.

'EXTENDED SILENCE IS UNUSUAL'

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

The report's English-language version carried a correction on Tuesday to say the report was based on a single unnamed source in North Korea, not multiple as it earlier stated.

It said his health had deteriorated since August due to heavy smoking, obesity and overwork, and he was now receiving treatment at a villa north of Pyongyang.

"It does look like something is going on, based on the repeated absences of last week," said Chad O’Carroll, CEO of the Korea Risk Group, which monitors North Korea.

"A health issue seems to be the most logical explanation for all this, but whether or not it's cardiac-related seems to be too early to tell."

On Tuesday, CNN reported an unidentified U.S. official saying the United States was "monitoring intelligence" that Kim was in grave danger after surgery.

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

Trump's national security adviser, Robert O'Brien, told Fox News on Tuesday the White House was monitoring the reports "very closely."

"There's lots of conjecture going around," a senior Trump administration official said on condition of anonymity late on Tuesday when asked if there was confirmation of the reports.

North Korea experts have cautioned that while hard facts about Kim's condition are elusive, his unprecedented absence from the celebrations for his grandfather's birthday signaled that something may have gone awry.