By Reem Shamseddine and Katie Paul

RIYADH (Reuters) - Saudi King Salman appointed two new ministers on Saturday to key security and economic posts, removing one of the royal family's most prominent members as head of the National Guard and boosting the kingdom's young crown prince.

The king also announced the creation of a new anti-corruption committee chaired by Crown Prince Mohammed bin Salman which Al Arabiya TV said had already detained 11 princes, four current ministers and tens of former ministers. The suspects were not named.

The cabinet reshuffle saw Prince Miteb bin Abdullah replaced as minister of the National Guard by Khaled bin Ayyaf, while Economy Minister Adel Fakieh was removed in favour of his deputy Mohammed al-Tuwaijri, according to a royal decree carried by state-run media.

Prince Miteb, the preferred son of the late King Abdullah, was once thought to be a leading contender for the throne before the unexpected rise of Prince Mohammed two years ago.

He had inherited control of the National Guard, an elite internal security force built out of traditional tribal units, from his father, who ran it for five decades.

Prince Miteb was the last remaining member of Abdullah's branch of the family to hold a position in the upper echelons of the Saudi power structure.

The move consolidates Crown Prince Mohammed's control of the kingdom's security institutions, which had long been headed by separate powerful branches of the ruling family.

Prince Mohammed, the king's 32-year-old son, already serves as defence minister and was named heir to the throne in a June reshuffle that sidelined his older cousin, Prince Mohammed bin Nayef who had also served as interior minister.

He has been responsible at the same time for running Saudi Arabia’s war in Yemen, dictating an energy policy with global implications and behind the plans for the kingdom to build a future after oil.

Prince Mohammed, who has pledged to go after graft at the highest levels, will now also head up the new anti-corruption body, which was given broad powers to investigate cases, issue arrest warrants and travel restrictions, and freeze assets.

"The homeland will not exist unless corruption is uprooted and the corrupt are held accountable," the royal decree said.

NEW ECONOMY MINISTER

The country's new economy minister, Tuwaijri, is a former Saudi air force pilot and former chief executive of HSBC’s Middle East operations who has led the economy ministry's programme to privatise some $200 billion of government assets.