Royal officials say Thailand's 88-year-old King Bhumibol Adulyadej, who marks the 70th anniversary of his coronation on Thursday, has had an operation to clear an artery.

The Royal Household Bureau said the procedure to insert a stent was conducted Tuesday with satisfactory results after tests determined that there was an inadequate supply of blood to the muscles of his heart.

The announcement also said there had been a decrease in cerebrospinal fluid putting pressure on his brain, a condition for which he began receiving treatment last month.

The king's health is a matter of intense national concern because of uneasiness about political stability during the succession.

The king, the world's longest reigning monarch, has been hospitalized for much of the past decade.