Saudi King Abdullah's unprecedented decision to appoint a second heir to his throne appears aimed at ensuring a smooth succession in a region thrown into turmoil by the Arab Spring.
It also opens the door for the next generation to step up, in an ultra-conservative state ruled for decades by ageing monarchs.
The 90-year-old monarch took the surprise measure Thursday naming his youngest half-brother Prince Moqren bin Abdul Aziz as a second heir, next in line after the ailing Crown Prince Salman.
In effect, he stripped Prince Salman of the customary right to name his own successor.
The king's decision was passed by three quarters of the Board of Succession, established by King Abdullah himself in 2006 to institutionalise the process of transition.
The council would normally exercise its prerogatives after the monarch's death.
King Abdullah wants to assure a rapid succession by this internal reorganisation of power" within the family, a source told AFP, adding that the decision had been "taken in agreement with Crown Prince Salman".
The source said the king also informed the board of his intention to appoint his son Mitab as second deputy premier.
The king wants to prepare his son, who is currently the minister of the National Guard, to be next in line of succession after Moqren, the same source said.
The decision came on the eve of a visit by US President Barack Obama, who was expected to advise the Saudi authorities to bring new blood into their ageing leadership, according to diplomats.
Obama is expected to discuss with his hosts ways to "assure a smooth transition as the rulers of the kingdom grow old and suffer health problems," a diplomat told AFP.
"The Americans do not like surprises in this country, which is the world's top oil exporter, and has an impact on the international oil market" he added.
Another diplomat stressed that "the stability of the kingdom is a priority for the United States."
But Saudi columnist Abderrahman al-Rashed insisted that President "Obama has no right to decide for the Saudis how to manage their affairs."
The kingdom is "more capable than its American friends think in sorting its internal affairs," he wrote in Asharq Al-Awsat newspaper.
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- Pass on baton -
In May last year, King Abdullah upgraded the National Guard, the kingdom's parallel army seen as a pillar of the ruling royals, to a ministry and appointed Sandhurst-educated Prince Mitab its head.
Analysts believe the old guard in the Al-Saud dynasty will have to pass the baton to a new generation, the grandsons of the kingdom's founder.
The oil-rich Gulf kingdom has grown "more aware of the need for a quick decision concerning the process of succession," said Asharq Al-Awsat.
The king wants to "protect the country from unpleasant and unexpected developments," read the editorial in the paper close to the ruling circle.
"Saudi Arabia is in the middle of a troubled and severely agitated region. Some states have collapsed and others are on the verge of collapsing," it said.
Under the usual rules of succession, power passes from brother to brother under the right of primogeniture among the sons of Abdul Aziz bin Saud, the kingdom's founder.
Crown Prince Salman, 79, is reputed to be ill and might not claim the throne at all, according to a source close to the circle of power.
The king's decision could still trigger a succession battle, according to Simon Henderson, director of the Gulf and Energy Policy Programme at the Washington Institute.
"This announcement was just a skirmish in the House of Saud. It may yet become a major political battle," he said.
"King Abdullah seems to have been concerned about the health of Crown Prince Salman and may have wanted to out-manoeuvre Salman's supporters who don't seem prepared to admit to his weaknesses," he told AFP.
Moqren, 69, had already moved a step in the direction of the throne when the monarch appointed him last year as the second deputy prime minister.
Prior to that, he served as the head of intelligence for seven years. He is one of the principal "confidants" of King Abdullah, diplomats said.