Saudi Arabia has replaced intelligence chief Prince Bandar bin Sultan, the kingdom's pointman on the Syrian conflict, "at his own request", according to the official news agency.

In a royal decree, Bandar was "exempted ... from his position at his own request" and replaced by his deputy, Yousef al-Idrissi, the news service reported on Tuesday.

Bandar, a former ambassador to the US, is widely regarded as among the most influential power brokers in the Middle East.

But he went abroad for several months for health reasons, with diplomats saying he had been sidelined in Saudi efforts to support rebels battling Syrian President Bashar al-Assad's government.

They said the responsibility has been transferred to the interior minister, Prince Mohammed bin Nayef, who cracked down on al-Qaeda following a wave of deadly attacks in Saudi Arabia between 2003 and 2006.

Bandar's management of the Syria issue had prompted American criticism, diplomats said.

Bandar himself reprimanded the US for its decision not to intervene militarily in Syria, and for preventing its allies from providing rebels with much-needed weapons, according to diplomats.

Media run by the Syrian regime and its allies in Lebanon have repeatedly criticised Bandar, accusing him of supporting Sunni Islamist fighters in Syria.