Saudi Arabia's King Abdullah on Monday issued a royal decree naming his half-brother Prince Salman as heir to the throne following the death of crown prince Nayef.
The monarch appointed Salman "crown prince and deputy prime minister" while also keeping him on as defence minister, said the decree published by the state news agency SPA.
In a simultaneous decree, the monarch promoted Prince Ahmed bin Abdul Aziz to take over from Nayef as interior minister, the SPA said.
Salman, 76, became defence minister in October following the death of Sultan, the then crown prince and long-serving defence and aviation minister, while Nayef was named heir to the throne.
It was the first ministerial post for Salman who had been the governor of Riyadh for around 50 years.
Nayef died on Saturday in Switzerland of "cardiac problems," a medical source in Geneva said.
The kingdom's security czar, who was behind an iron-fisted crackdown on Al-Qaeda following a wave of attacks in the kingdom between 2003 and 2006, had frequently travelled abroad for medical treatment.
By appointing Salman, King Abdullah is following the tradition of keeping top posts in the hands of the first generation of the sons of Abdul Aziz, founder of the desert kingdom.
King Abdullah in 2006 established the Allegiance Council, a commission of 35 senior princes, as a new mechanism to name heirs to the throne of the Gulf oil powerhouse in the long term.
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But the royal decree showed on Monday that the monarch had taken his decision "after consulting the law of allegiance" without any reference to debating his choice in the council.
He did the same when he named Nayef crown prince, since the new system of selecting an heir is not supposed to come into force during King Abdullah's reign.
Salman is the 25th son of Abdul Aziz and one of seven full brothers known as the "Sudairi Seven," after their influential mother Hassa bint Ahmad al-Sudairi. The seven included the late king Fahd and princes Sultan and Nayef.
In addition to Salman, remaining Sudairis include Prince Abdul Rahman, Prince Turki and Prince Ahmed, who was deputy interior minister before being assigned the portfolio.
Most of the senior members of the Al-Saud dynasty are ageing, increasing pressure on the family to pass the reins to a younger generation.
Ailing King Abdullah is 88, while his half-brothers Sultan and Nayef died at 86 and 79 respectively within the space of a year.
Prince Ahmed has served as deputy interior minister since 1975. The eldest son of Prince Nayef, Prince Mohammed, has been assistant to the minister for security affairs since 1999.
Seen as more conservative than King Abdullah, Nayef was a staunch defender of the Saudi dynasty and resisted any opposition, especially from the Shiite minority in the eastern province.
He also strongly opposed allowing women to drive.