Saudi Arabia's King Abdullah bin Abdulaziz is suffering from pneumonia and temporarily needed help to breath through a tube on Friday but the procedure was successful and his condition was now stable, the royal court said.

The elderly monarch was admitted to the King Abdulaziz Medical City in Riyadh on Wednesday for tests after he suffered what one source described as breathing difficulties, state media said.

"It became apparent that there was a lung infection that required the insertion of a tube to aid with breathing on a temporary basis this evening," the royal court said in a statement carried by state news agency SPA.

The procedure had resulted in "stability and success," it added.

A Saudi source familiar with the affairs of the royal family said the king would most likely stay in hospital for another week.

Markets keep a close eye on the health of the king of the world's top oil producer, a country that also has influence over Muslims through its guardianship of Islam's holiest sites.

King Abdullah, who took power in 2005 after the death of his half-brother King Fahd, is thought to be 91, although official accounts are unclear. He has undergone surgery in the past few years related to a herniated disc.

Abdullah named his half-brother, Prince Salman, 13 years his junior, heir apparent in June 2012 after the death of Crown Prince Nayef bin Abdulaziz. Last year he appointed Prince Muqrin bin Abdulaziz as deputy crown prince, giving some assurance on the kingdom's long-term succession process. – Reuters