WASHINGTON (AFP) - US President Donald Trump wished North Korea's Kim Jong Un "well" on Tuesday (April 21) but stopped short of directly commenting on the reclusive leader's health amid reports he underwent serious surgery.

"I wish him well," Mr Trump told reporters at the White House, noting the "good relationship" he shares with the North Korean leader.

"If he is in the kind of condition that the reports say, that the news is saying, it's a very serious condition."

South Korea had played down a report on Tuesday that Mr Kim was being treated after surgery, as speculation mounted over his absence from a key anniversary. Pyongyang marked the birthday of its late founder, Mr Kim's grandfather Kim Il Sung, on April 15 - by far the most important date in its annual political calendar - but Mr Kim was not seen in attendance.

Daily NK, an online media outlet run mostly by North Korean defectors, said Mr Kim had undergone a cardiovascular procedure earlier this month and was recovering at a villa in North Phyongan province. "Excessive smoking, obesity, and fatigue were the direct causes of Kim's urgent cardiovascular treatment," it cited an unidentified source inside the country as saying.

No confirmation of the report was immediately available. But it triggered widespread speculation, with CNN citing a US official saying that Washington was "monitoring intelligence" that Mr Kim was in "grave danger" after undergoing surgery.