U.S. President Donald Trump listens to a speaker during the daily briefing on the novel coronavirus in the Brady Briefing Room of the White House in Washington, DC, April 23, 2020. AFP

US President Donald Trump on Thursday rejected reports that North Korean leader Kim Jong Un was ailing, criticizing his frequent nemesis CNN for running the story.

"I think the report was incorrect, let me just put it that way," Trump told reporters. "I'm hearing they used old documents."

Trump declined to say if he had direct knowledge from North Korea that Kim was fine.

He instead attacked cable news network CNN, with which the US leader has an acrimonious relationship.

"I think it was a fake report done by CNN," Trump said at a daily briefing on the coronavirus pandemic, before refusing to take further questions from a journalist of the network.

CNN, quoting what it said was an anonymous US official, on Monday reported that Washington was "monitoring intelligence" that Kim was in "grave danger" after undergoing surgery.

Daily NK, an online media outlet run mostly by North Korean defectors, separately said that Kim underwent a cardiovascular procedure earlier this month and was recovering at a villa in North Pyongan province.

It said that Kim, who is in his mid-30s, had needed urgent treatment due to heavy smoking, obesity and fatigue.