Saudi King Salman will undergo treatment at Al Salam Palace in Jeddah for a lung inflammation, the state news agency said on Sunday, hours after he underwent medical tests.

Citing the royal court, the state news agency said the 88-year-old king would be treated with antibiotics until the inflammation subsides.

Due to King Salman’s health issue, Crown Prince Mohammed bin Salman, the de facto Saudi leader, postponed a visit to Japan that had been scheduled to begin on Monday, Japan’s Chief Cabinet Secretary Yoshimasa Hayashi said.

“Saudi Arabia informed the Japanese government that due to the health condition of King Salman of Saudi Arabia, Crown Prince Mohammed’s visit to Japan, which had been scheduled to begin on the 20th, had to be postponed,” Hayashi said at a news conference in Tokyo.

Earlier on Sunday, King Salman underwent medical tests at the royal clinics at Al Salam Palace due to “high temperature and joint pain”, the Saudi state news agency said.

The king was last admitted to hospital in April for a routine checkup, state TV reported then.

King Salman, the custodian of Islam’s holiest sites, became ruler of the world’s top oil exporter in 2015 after spending more than 2-1/2 years as the crown prince and deputy premier.

His illness struck just as the crown prince met with U.S. National Security Adviser Jake Sullivan in the kingdom for talks on a strategic agreement between Washington and Riyadh.

Saudi Arabia’s embassy in Japan did not immediately respond to a request for comment about the crown prince’s cancelled trip. He had been set to meet with Japanese Emperor Naruhito and Prime Minister Fumio Kishida during the trip scheduled from May 20-23.