Thailand's royal palace says the country's 86-year-old king is continuing to suffer from an infected colon, a month after he underwent surgery to remove his gallbladder.

King Bhumibol Adulyadej, the world's longest reigning monarch, was admitted to a Bangkok hospital last month with an inflammation of his gallbladder, which was removed through laparoscopic surgery.

The palace said in a statement Thursday that the king continues to have diverticulitis, an infection of pouches formed in the wall of the lower part of the large intestine. It said doctors have given him a new type of intravenous antibiotic and that his fever has declined.

They said his overall condition has improved but that doctors will give him antibiotics for a longer period of time.