Monaco's Prince Rainier has been moved to intensive care after a lung infection for which he was hospitalized earlier this month took a turn for the worse.

Palace officials said Tuesday the health of the 81-year-old prince has worsened after several days of improvement.

The officials said the prince had been reacting well to treatment for his lung problems since his hospitalization March 7.

The prince has suffered a series of health setbacks in recent years.

He has ruled the tiny but wealthy state on the French Riviera since 1949. His wife, the late Hollywood star Grace Kelly, died in a car crash in 1982.

Prince Albert, the ruler's 47 year-old son, is Monaco's crown prince.