Saudi Arabia's rulers have launched a fundraising drive to raise money for Syrians displaced by the five year civil war - including those recently forced to flee eastern Aleppo after a government offensive backed by Riyadh's regional rival and arch geopolitical nemesis, Iran.

The country's state-owned media arm, the Saudi Press Agency (SPA) announced late on Monday that King Salman bin Abdulaziz had already allocated $27 million from Riyadh's budget, as well as kicking in over $5m of his own money to help Syrian refugees driven from their homes by fighting.

His brother, Crown Prince Mohammed bin Nayef, has committed $2.6m while his son, Deputy Crown Prince Mohammed bin Salman, has contributed $2.1m.

"The Custodian of the Two Holy Mosques, King Salman bin Abdulaziz al-Saud, has ordered a popular campaign to be launched ... to provide relief for the brotherly Syrian people," SPA said.

It added that the funds would be used to set up a refugee camp, but did not specify where. Saudi Arabia and the other states of the Gulf have been criticised for not taking in enough Syrian refugees when its neighbours - Lebanon, Jordan and Turkey - have taken in over four million.

The Saudis have found themselves very much on the back foot in Syria, where they have long funded and supported Sunni rebel groups seeking to overthrow Assad, who is backed by their major rival, Iran. Assad's success against rebels in Aleppo - which he retook with Russian backing earlier this month - has been a crushing blow to the Sunni-led rebellion against him.