RIYADH // Saudi Arabia’s King Abdullah on Saturday sacked the deputy defence minister, Prince Khaled bin Bandar bin Abdul Aziz, just a month and a half after appointing him.

A royal decree cited by the official SPA news agency said the decision was taken at the request of Crown Prince Salman bin Abdul Aziz, who is the defence minister.

The reasons for the move were not immediately known, and no successor was announcewd for Prince Khaled, who was appointed to the post on May 14.

Saudi Arabia has been on alert following turmoil in Iraq where Sunni Islamist militants have seized control of major cities from the Shiite Muslim-led government of Prime Minister Nouri Al Maliki.

On Thursday, King Abdullah instructed authorities in the oil-rich kingdom to take “necessary measures” to defend it from Islamist militants battling the Baghdad government.

Moves in the ruling family are closely watched at home and abroad for clues to who will rule the world’s top oil exporter, a country that also has a huge influence over Muslims through its guardianship of Islam’s holiest sites.

Prince Khaled was moved to the post of deputy defence minister in May when King Abdullah removed him from his position as governor of Riyadh Province and appointed his son, Prince Turki, in his place.

The move was seen as strengthening the grip of his branch of the ruling dynasty as it approaches a difficult decision over how to transfer power to the next generation.

King Abdullah, who is over 90, has made a series of changes and appointments over the past two years that have consolidated the position of his allies in the family.

The most recent was the appointment of Prince Muqrin, a former intelligence chief, as deputy crown prince.

The newly created position made Prince Muqrin, the youngest son of the kingdom’s founder, King Abdulaziz Al Saud, next in line to succeed in the world’s top oil exporter and birthplace of Islam after his half-brothers King Abdullah and Crown Prince Salman.

* Agence France-Presse and Reuters