Saudi Arabia's 84-year-old ruler King Salman bin Abdulaziz has been admitted to King Faisal Specialist hospital in the capital Riyadh for medical checks, the state news agency (SPA) reported early on Monday.
It said the king, who has ruled the world's largest oil exporter and the close US ally since 2015, was admitted for inflammation of the gallbladder, without giving further details.
King Salman spent more than 2-1/2 years as the Saudi Crown Prince and deputy premier from June 2012 before becoming king.
He had also served as the governor of Riyadh region for more than 50 years.
The 34-year-old Crown Prince, Mohammed bin Salman, widely known by his initials MbS, is the defacto ruler and has introduced a raft of reforms to transform the kingdom's economy and end its "addiction" to oil.