Prince Rainier, the ruler of Monaco, is in the intensive care unit of a hospital in his wealthy statelet on the French Riviera in a condition described as "stable", sources said.

　　The 81-year-old prince was on Tuesday rushed into the resuscitation ward of Monaco's cardio-thoracic centre after his health abruptly and dramatically deteriorated. He was admitted to the centre March 7 for treatment of a recurrent respiratory problem.

　　According to France's Europe 1 radio station, the principality's archbishop and its parish priest went to Prince Rainier's bedside on Monday, raising speculation that the ruler -- one of the world's longest-reigning monarchs -- was at death's door.

　　The sources, declining to be identified, would not give details as to Prince Rainier's condition beyond saying it was "stable", or unchanged since he had been taken to the intensive care unit.

　　A health bulletin was to be issued later Wednesday.

　　A statement from the palace on Tuesday said: "After several days of care which saw a clear improvement, a relapse of a lung infection has required a transfer to the intensive care unit."

　　Rainier's three children -- his heir Prince Albert and daughters Caroline and Stephanie -- rushed to his bedside. Caroline came from Paris and Albert from Italy, a family source said.

　　Prince Albert is next in line to take power in Monaco when Prince Rainier dies. His father increasingly delegated responsibilities to him over the past few years, as heart and respiratory problems took an ever bigger toll on his duties as ruler.

　　Prince Rainier's cardiac ailments first came to light in 1994, when he was given a double bypass. Since then, he has been admitted to hospital five times.

　　Prince Rainier III ascended to power in the tiny Mediterranean territory in 1949, three years before Queen Elizabeth II took the throne of England.

　　He became the darling of the jet set, and the people columns of the world media, when he married the US film star Grace Kelly in 1956.

　　She was to bear him his three children before dying in a car crash in the principality in 1982.