Saudi Arabia's King Salman bin Abdulaziz Al Saud is set to undergo treatment after being diagnosed with a lung inflammation, the state news agency said Sunday.

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 postponed a visit to Japan that had been scheduled to begin Monday, Japan's Chief Cabinet Secretary Yoshimasa Hayashi said.

Earlier Sunday, King Salman underwent medical tests at the royal clinics at Al Salam Palace due to "high temperature and joint pain," the 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.