Saudi Arabia's King Abdullah has appointed Interior Minister Prince Nayef as the new crown prince, the Royal Court said in a statement issued on Friday, signalling an orderly process of future succession in the world's largest oil exporter.

"We chose His Royal Highness Prince Nayef bin Abdulaziz as crown prince," said the statement, read on state television and carried on the kingdom's news agency SPA soon after midnight.

It said Nayef, who is in his 70s, was appointed after King Abdullah took his choice to a royal family body called the Allegiance Council, set up in 2006 to make the process of succession in the conservative Islamic nation smoother and more orderly.

It was the first time the council had been involved in the appointment of a new crown prince, a move that analysts had said would help to regulate an opaque system of succession.

Crown Prince Sultan died of colon cancer in New York almost a week ago. He was also the kingdom's defence and aviation minister for nearly five decades. No replacements for these positions have yet been appointed.

Just over a century ago, King Abdulaziz Ibn Saud recaptured the family's historical stronghold of Riyadh from a rival clan, setting his family on a path of conquest from the Red Sea to the Gulf that eventually made the sleepy oasis town the capital of the world's foremost oil power.  Prince Nayef has been the interior minister since 1975, a post to which he was reappointed in the Royal Court statement.

In recent years he has run the kingdom on a day-to-day basis when King Abdullah and Prince Sultan were both absent. King Abdullah's recurrent back problem has caused him to go abroad for medical treatment.     

Nayef, a half-brother of King Abdullah, was born around 1933 in Taif, the pretty mountain town where the royal court repaired each year to escape the stifling summer of the capital Riyadh and the second city Jeddah.

Saudi Arabia had only a year earlier come into being after Nayef's father King Abdulaziz Ibn Saud united the Bedouin tribes behind his vision of a pure Islamic state and conquered much of the Arabian Peninsula.

Growing up in the royal court of the 1930s and 1940s, Nayef is of the last generation of Saudis who knew the austere desert kingdom before the first flush of oil wealth changed it beyond all recognition.   

As interior minister, Nayef led a successful effort to end a wave of Al Qaeda attacks inside the kingdom from 2003.   

Television footage on Saudi news channels on Thursday showed some leading members of the Al-Saud family receiving mourners for Crown Prince Sultan at the Yamama Palace in Riyadh.  - Reuters