Saudi Arabia's King Abdullah has been hospitalized in the capital, Riyadh, to undergo back surgery following two similar operations last year in the United States.

The Saudi state news agency said the king arrived at the King Abdulaziz Medical City earlier Sunday. The procedure, announced last week, will tighten a slackening ligament around his third vertebra.

The health of the ruler of the world's leading oil exporter is closely followed, given his age and the concentration of power among Saudi Arabia's ruling royal family. The king is thought to be in his late 80s.

King Abdullah was absent for three months late in 2010 while he underwent treatment in New York for a herniated disc that caused blood to accumulate around his spine. That surgery and a second, follow-up procedure were declared successful.

During the king's stay in the U.S. and his convalescence in Morocco, his brother – Crown Prince Sultan – was in charge of governing the kingdom.