The Kingdom of Saudi Arabia named the Muslim Brotherhood and two other Islamist groups fighting Bashar Assad's rule in Syria as terrorist groups. They also ordered individuals from the Kingdom who have flooded into Syria since the revolution began, to come home in 15 days or face imprisonment.

AFP:

The move represents a major escalation against the Brotherhood of deposed Egyptian president Mohamed Morsi and indicates rising concern in Riyadh over the potential risks to domestic security of Saudi extremists fighting in Syria.

Riyadh staunchly supports Sunni-led rebels battling to overthrow Syrian President Bashar al-Assad but has long feared blowback from radical jihadist groups, particularly after a spate of attacks by a local Al-Qaeda franchise from 2003 to 2006.

Friday's move comes two days after Saudi Arabia, Bahrain and the United Arab Emirates recalled their ambassadors from Qatar, which supports Islamists groups in the region and was a backer of the Brotherhood.

A list published by the interior ministry designates as terrorist organisations the Brotherhood, Al-Nusra Front, which is Al-Qaeda's official Syrian affiliate, and the Islamic State of Iraq and the Levant (ISIL), a rogue group fighting in both Syria and Iraq.

Also blacklisted are Shiite Muslim rebels known as Huthis in northern Yemen and "Hezbollah inside the kingdom," a reference to a little-known Shiite group in` overwhelmingly Sunni Saudi Arabia.

The interior ministry, in a statement carried by state media, said it will prosecute anyone backing these groups "financially or morally", or who express sympathies for them or seek to promote them through media and social networks.

It also forbids "participation in, calling for, or incitement to fighting in conflict zones in other countries."

Saudis fighting abroad were given a 15-day ultimatum Friday to return home or face imprisonment.

Prison also awaits anyone calling for demonstrations or taking part in them, the ministry said.

And analysts warned of the effect of that on civil liberties.

"There is fear that the text will be interpreted in such a way to muzzle freedom of expression," said sociologist Khaled al-Dakheel.

Last month, King Abdullah already announced jail terms of up to 20 years for belonging to "terrorist groups" and fighting abroad and tough sanctions for anyone backing the incriminated organisations.

Rights group Amnesty International sharply criticised that decree, saying it could be used to suppress peaceful political dissent because the law used an "overly vague definition of terrorism."

The Saudis are apparently trying to clean up the opposition to Assad while guarding against a terrorist boomerang at home. King Abdullah has come under increasing pressure from the west to refrain from supplying arms to designated terrorist groups. The move by the Gulf states to pressure Qatar to stop funding Syrian terror groups may also be part of an effort to make it easier for the west to supply better weapons to Syrian rebels.

One problem with the new Saudi policy is that al-Nusra is probably the most effective military force fighting against Assad. Cutting them off weakens the overall effort to defeat the Syrian government and their Hezb'allah allies. Evidently, Abdullah thought the danger to the Kingdom outweighed any advantages on the ground that al-Nusra gave the anti-Assad forces.