Uncertainty about the longevity of Saudi Arabia’s king intensified on Friday with the announcement that he was battling pneumonia and needed temporary help from a breathing tube.

While a statement from the Saudi royal court said the king, Abdullah, was in stable condition at a hospital, there was no immediate word on his prognosis or a discharge date.

The king, who turned 90 in August, has a history of medical problems, and his health is often scrutinized for any hint of a leadership change in Saudi Arabia, an absolute monarchy and regional American ally that is perhaps the world’s most important oil producer.

The royal court, in an announcement quoted by the official Saudi Press Agency, said a lung infection had been diagnosed in the king after he was admitted to King Abdulaziz Medical City Hospital in Riyadh, the capital, on Wednesday. Other news services said he was transferred on Thursday to a military hospital.