Updated

A hospital official says Saudi King Abdullah has undergone successful back surgery in the fourth such operation in nearly two years on the 87-year-old monarch.

The official said Saturday's surgery at the King Abdel Aziz medical compound in Riyadh sought to secure a loose vertebra. The official spoke on condition of anonymity because he is not authorized to brief the media.

Although the operation was described as successful, it raises questions about the overall health of one Washington's most critical allies in the Middle East.

The king had two back surgeries in New York — one in 2010 for a slipped disk and a blood clot pressing on nerves in his back and a second to stabilize vertebrae in 2011. The third back surgery was in Riyadh later in 2011.