Prince Mohammed's father, King Salman, issued a royal decree deputising his son to "manage state affairs and guard the interests of the people" during the monarch's "personal break", state news agency SPA reported.
On June 21, King Salman stripped the title of crown prince from his nephew Mohammed bin Nayef, naming 31-year-old Prince Mohammed, often known as MBS, as heir to the throne.
The crown prince has earned a reputation as a reformist in the ultra-conservative kingdom but is seen by some as lacking experience.
Qatar has denied the allegations.
The suspension of diplomatic and trade ties with Qatar has sparked the largest crisis to ever hit the Gulf Cooperation Council.
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