BANGKOK (REUTERS) - Thailand's King Bhumibol Adulyadej, the world's longest-reigning monarch, is making a recovery in hospital after being treated for a blood infection and lung inflammation, the palace said on Wednesday (Sept 16).

The 87-year-old King Bhumibol has been in Bangkok's Siriraj hospital for more than three months and had been treated for water on the brain. He was suffering at the weekend from a blood infection and lung inflammation.

His fever has subsided, blood oxygen levels had returned to normal and an X-ray had shown his lung inflammation had been lowered substantially, the palace said.

The king was still receiving food intravenously and was being given oxygen, it said.

The king's health is watched closely in Thailand, where he is a figure of moral strength and symbol of continuity in a country that has been through much upheaval during his 69-year reign.

The king has spent most of the past six years in hospital.

Most Thais have known no other monarch, and nervousness over the eventual succession has played into a decade of political division.

During a visit to a royal foundation for volunteer doctors on Monday, covered by Thailand's daily royal news programmes, the king's youngest daughter, Princess Chulabhorn, urged people to pray for the his recovery.

"I would like all of you to think of the king while praying, that you're praying for his recovery from illness and for him to live long," she said.