Trump says reports on Kim's health 'incorrect'

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

"I think the report was incorrect, let me just put it that way," Trump told reporters on Thursday.

"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 Phyongan province.

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

Trump's denial of the report came two days after he declined to comment, saying only that he wished Kim well.

South Korea, which is still technically at war with the North, earlier said it could not confirm the reports on Kim and reported no unusual movements in its neighbour.

Trump has met Kim three times in historic summitry and has voiced admiration for him, although hopes have dimmed for reaching a comprehensive agreement.

"I hope he's not in medical trouble. I hope he's not. I have gotten along very well with him. Remember you would have been in a war with North Korea if I didn't get elected president," Trump said on Thursday.

Trump declined to say when he was last in touch with Kim, saying: "We have a good relationship with North Korea, as good as you can have."