JEDDAH (Reuters) - Saudi King Abdullah, who underwent surgery last year for back-related problems, will undergo an operation in the coming days, Saudi Arabia's state news agency reported on Tuesday. The health of the ruler of the world's leading oil exporter is of keen interest, given his age - thought to be 88 - and the concentration of power among Saudi Arabia's ruling royal family. "In continuation of the scheduled medical follow up of King Abdullah, the king will undergo an operation in the coming days in Riyadh," news agency SPA reported, citing a statement from the royal court.