King Salman will undergo a treatment programme 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 postponed a visit to Japan that had been scheduled to begin on Monday, Japan's Chief Cabinet Secretary Yoshimasa Hayashi said.
Earlier on 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.
U.S. President Donald Trump fired General Timothy Haugh as director of the National Security Agency on Thursday, according to two officials familiar with the decision, and congressional Democrats denounced the removal of the nonpartisan official from a top security post.
Israel stepped up airstrikes on Syria, declaring the attacks a warning to the new rulers in Damascus as it accused their ally Turkey of trying to turn the country into a Turkish protectorate.
The Trump administration moved forward with the sale of more than 20,000 US-made assault rifles to Israel last month, according to a document seen by Reuters, pushing ahead with a sale that the administration of former president Joe Biden had delayed.