The people of Thailand celebrated King Bhumibol Adulyadej's 87th birthday Friday with both joy and trepidation, as the ailing monarch failed to make an expected public appearance at a time when there is growing concern over how the country will manage a smooth succession at the end of his reign.

An announcement issued by the palace late Thursday night said the king's doctors advised he should not attend the main morning ceremony for his birthday because of poor health. His son, the heir apparent, substituted for him at an afternoon religious ceremony.

The king, who has reigned since 1946, has been hospitalized since early October when he had his gall bladder removed. - AP