Thailand's royal palace says 88-year-old King Bhumibol Adulyadej, the world's longest-reigning monarch, is suffering from a 38.1 C (100.6 F) fever, fatigue, rapid breathing and occasional high blood pressure.

The king has lived in a Bangkok hospital for much of the past six years, and Tuesday's health bulletin described the same general set of symptoms that he has been suffering for six months.

The king has been a stabilizing figure through much of his reign, but his participation in public affairs has sharply declined in recent years.

The health bulletin said blood tests showed the king was suffering from an infection of an unknown cause. It said the king was being given antibiotics and oxygen and treatment to remove excess saliva and phlegm.