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.
Progress is stalling at talks aimed at securing a ceasefire in Gaza, with the sides divided over the extent of Israeli forces' withdrawal from the Palestinian enclave.
North Korean leader Kim Jong Un told Russia's top diplomat his country was ready to "unconditionally support" Moscow's every effort to resolve the conflict in Ukraine, state media reported on Sunday, as the two countries held high-level strategic talks.
A preliminary report depicted confusion in the cockpit shortly before an Air India jetliner crashed, killing 260 people last month, after the plane's engine fuel cutoff switches almost simultaneously flipped, starving the engines of fuel.
US President Donald Trump defended the state and federal response to deadly flash flooding in Texas on Friday as he visited the stricken Hill Country region, where at least 120 people, including dozens of children, perished a week ago.