Japan's top government spokesman said Monday a planned visit this week by Saudi Arabia's Crown Prince Mohammed bin Salman has been postponed "due to the health condition of King Salman".
The announcement came hours after the Royal Court in Riyadh said Prince Mohammed's 88-year-old father had a lung infection and was undergoing treatment involving antibiotics.
Prince Mohammed had been due to meet Prime Minister Fumio Kishida and the Japanese emperor on his trip from Monday, which would have been his first to Japan since 2019.
But Saudi Arabia's government informed Tokyo late on Sunday that, due to King Salman's health, the visit had been postponed, Yoshimasa Hayashi told reporters.
"The visit of His Royal Highness Crown Prince Mohammed to Japan will be re-coordinated between the two countries," Hayashi said.
Saudi sources told AFP on Monday that members of the delegation would still travel to Japan for some talks.
King Salman has been on the throne since 2015, though his 38-year-old son was named crown prince in 2017 and acts as day-to-day ruler.
Saudi Arabia, the world's biggest crude exporter, has for years sought to quell speculation over King Salman's health, which is rarely discussed.
But the Royal Court disclosed in April that he had been admitted to King Faisal Specialist Hospital for "routine examinations". He left the hospital later the same day.
Before that, his most recent hospitalisation had been in May 2022, when he went in for a colonoscopy and stayed for just over a week.
The court had said earlier on Sunday the king was suffering from "high temperature" and joint pain and would undergo medical tests.
Japan's Kishida visited Saudi Arabia last July and the focus of his talks with Prince Mohammed was on energy, particularly around green energy and decarbonisation.
This time "energy security and clean energy" as well as "soft power exchanges", economic diversification and foreign affairs were on the agenda, the foreign ministry had said.
Analysts had said Prince Mohammed, known by his initials MBS, would also be on the lookout for more opportunities in gaming as he seeks to improve Saudi Arabia's image.
The reputed "Call of Duty" fan has launched a multi-billion-dollar push into the gaming sector, from eSports to game development, as part of his Vision 2030 transformation strategy for the oil-rich kingdom.
Saudi Arabia's sovereign wealth fund holds a stake of around eight percent in Nintendo, and the country is planning a theme park based on Japan's "Dragon Ball" manga franchise in a new "entertainment city" outside Riyadh.