Saudi Arabia's King Abdullah has issued a royal decree that punishes citizens who fight in conflicts outside the kingdom, with prison sentences ranging from three to 20 years in jail.

The statement issued by the Saudi Royal Court on Monday states that anyone who took part in acts of killing outside the kingdom or joined extremist terrorist groups or supported them materially or verbally through incitement would also face imprisonment.

Syria's civil war has drawn young Saudis, encouraged by influential clerics and community members to fight President Bashar Assad's forces.

The royal court said the king's decree was issued in accordance with Islamic law to protect Muslim unity and security in Saudi Arabia.

The decree comes after a new counterterrorism law came into effect in the kingdom Sunday.