AVA- The move was announced Wednesday through decrees issued by the state-run SPA news agency.
The former crown prince and nephew of King Salman, Mohammed bin Nayef, was relieved of all of his positions including the role of interior minister, the decrees said.
Mohammed bin Salman, who had been the deputy crown prince, will also now be Saudi Arabia's deputy prime minister.
The 31-year-old has been in charge of the Saudi-led coalition fighting on behalf of Yemen's government in a war against Iran-backed Houthi rebels.
Saudi state media said Wednesday's changes were approved by 31 of the 34 members of the royal family who make up what is known as the Allegiance Council.
King Salman came to power in 2015 following the death of his half-brother, King Abdullah.