Saudi Arabia will imprison for three to 20 years any citizen who fights in conflicts abroad, according to a royal decree released through state media on Monday.

The decree also said Saudis who join or endorse groups it classifies as terrorist organisations, whether inside or outside the country, would face prison sentences of between five and 30 years.

It appeared to be another official move to discourage the kingdom's citizens from travelling to Syria to fight alongside rebels battling the government of President Bashar Al-Assad.

Saudi Arabia's Islamic religious authorities have previously spoken out against Saudi fighters going to Syria, but the Saudi Interior Ministry estimates that around 1,200 Saudis have gone there nonetheless.

Riyadh backs some rebel groups in Syria with money and arms, but is wary of allowing its citizens to go and fight there.

The ban on joining or endorsing groups it classifies as "terrorist" could potentially also apply to the Muslim Brotherhood or the Lebanese Shi'ite Muslim group Hezbollah, which has fighters on Assad's side in Syria. - Reuters