Prince Naif's designation came a day after doctors asked the king to rest due to a disc problem.

Crown Prince Sultan, deputy premier and minister of defense and aviation, is on private vacation in the Moroccan city of Agadir.

Naif, who is also chairman of the Supreme Haj Committee, has been in Makkah this week, supervising security arrangements for the annual pilgrimage, in which some two million Muslim pilgrims will gather in the holy city of Makkah.