Saudi Arabia's grand mufti - the highest religious authority in the birthplace of Islam - has urged young Saudis to refrain from fighting in Syria as the regime fears the return of battle-hardened fighters.

The kingdom has backed rebels battling President Bashar al-Assad calling on world powers to 'enable' Syrians to protect themselves.

However, the regime is wary that the experience fighters gain could mean they return home ready to wage war on their own dynastic rulers.

"This is all wrong, it's not obligatory," Sheikh Abdulaziz Al al-Sheikh said, in reference to Saudi men joining a civil war that is now well into its third year, according to pan-Arab daily al-Hayat.

"These are feuding factions and one should not go there. I do not advise one to go there ... Going to a land that you do not know and without experience, you will be a burden to them, what they want from you is your prayer."                          

It is not known how many Saudis have gone to fight in Syria.

Al-Qaeda fighters led by Osama bin Laden attacked targets in Saudi Arabia after war experience elsewhere.  

Islamists in Saudi Arabia, who follow a puritanical version of Sunni Islam, denounce President Assad and his administration as 'infidels' because of their roots in the Alawite sect, an off-shoot of Shia Islam.

"Muslim should be fearful of God and not deceive young Muslims and exploit their weakness and lack of insight and push them to an abyss," the mufti was quoted by the paper. 

The grand mufti, appointed by the Saudi king, also warned preachers against encouraging young men to fight in Syria during their sermons, after delivering what the paper said was a lecture on 'Deviation among the youth' at a mosque.

"I advise them (preachers) to advise (young people) as they would advise their sons," he added. 

Bin Laden led a battalion of Arab volunteers fighting against the Soviet forces occupying Afghanistan in the 1980s, while others joined local Muslim forces in civil wars in the 1990s in Bosnia and Chechnya.

But even before he sent 15 Saudis and four other Arabs to carry out the 11 September attacks on the US in 2001, Bin Laden had turned against Saudi Arabia's ruling al-Saud family, mainly because of its close relationship with the West.

That relationship, especially with its oldest ally the US has cooled somewhat over the past months over the failure to end the war in Syria and a softening of tone towards arch-rival Shia Iran.