Thailand's King Bhumibol Adulyadej, the world's longest-reigning monarch, has been hospitalized with fever and fatigue, the royal palace said Sunday.

King Bhumibol Adulyadej, 81, was admitted to a Bangkok hospital on Saturday night. Doctors are monitoring his condition while administering antibiotics and intravenous fluid, the statement from the Royal Household Bureau said.

Thailand abolished absolute monarchy in the 1930s, so the king wields little power although he last month appealed for unity amid Thailand's four-year-long political crisis. He remains a deeply revered figure and enjoys immense popularity.