Dozens of conservative Saudi Arabian clerics have called for Arab and Muslim countries to "give all moral, material, political and military" support to what they term a jihad, or holy war, against Syria's government and its Iranian and Russian backers.

Although the clerics who signed the online statement are not affiliated with the government, their strong sectarian and anti-Christian language reflects a growing anger among many Saudis over Russian and Iranian involvement in Syria's civil war.

Russia last week started air strikes against Syrian opposition targets. The Kremlin, a staunch supporter of the ruling Syrian regime of Bashar al-Assad, says it wants to weaken the militant group known as the Islamic State. Saudi Arabia, along with Turkey and other Gulf states, has supported rebels trying to unseat the Assad regime and has denounced the Russian attacks. The clerics' statement portrayed the Russian bombardments as part of an Orthodox Christian crusade.

"The holy warriors of Syria are defending the whole Islamic nation. Trust them and support them ... because if they are defeated, God forbid, it will be the turn of one Sunni country after another," the statement said.

The bloodshed in Syria, part of a wider struggle for regional supremacy between Sunni Muslim Saudi Arabia and Shi'ite Iran, has aggravated sectarian anger across the Middle East and drawn religiously motivated foreign fighters to both sides.