Morocco has largely avoided the Islamist-related violence rocking much of the region, but a recent Al-Qaeda video calling for jihad prompted authorities to react furiously, reflecting the kingdom's security fears.

The video, which also denounced corruption and lashed out at King Mohamed VI -- contrasting Morocco's sprawling slums with his vast wealth -- led to an independent journalist being arrested and charged with inciting terrorism for posting a link to the website of El Pais, which carried the video.

The government also threatened to prosecute the Spanish newspaper.

Analysts say the kingdom wants to reaffirm its zero tolerance policy towards jihadist activity, amid rising concerns about Moroccans being recruited to join Islamist fighters in Syria.

"The palace's reaction likely reflects its fears ... over the number of Moroccans joining the fight in Syria, since the kingdom was thought to be relatively insulated from the issue of foreign fighters and jihadist returnees," said Vish Sakthivel from the Washington Institute, a US think tank.

The number of Moroccan Islamists battling Syrian President Bashar al-Assad's regime is hard to know, but estimates run as high as 1,000, with around 90 having been killed so far, according to official figures.

North Africa expert William Lawrence underlines that this is a region-wide phenomenon, citing estimates of around 250 Algerians and 450 Tunisians thought to have been killed in Syria, raising concerns in both countries.

"The jihadists return to Morocco with training and new ideological hardening that poses a threat to the state ... So Morocco will do what it can to break up the recruitment that's going on, to prevent people from gaining experience who may come back," he said.

The authorities frequently claim to have busted Al-Qaeda linked cells, highlighting the domestic threat as well as Morocco's success in limiting the ability of homegrown extremists to organise, through its tough policy of preventive security.

Just last month, a court in Rabat's twin city of Sale jailed nine young Moroccans belonging to Ansar al-Sharia in the Islamic Maghreb, who were arrested in late 2012 and accused of planning attacks on strategic sites in several cities.

Morocco prides itself on being a country with a moderate version of Islam, whose king is accorded the official title of Commander of the Faithful, and where stability prevails in a region racked by insecurity.

The image of stability and tolerance is of heightened importance given the country's reliance on Western tourists to supply the hard currency needed to prop up its ailing economy.

But the kingdom is no stranger to jihadist violence, having suffered two major suicide attacks in the past decade, one in Casablanca in 2003 that killed 33 people, and the other in Marrakesh in 2011, which killed 17 people.

Now observers say Salafism, the ultra-conservative brand of Sunni Islam which has enjoyed a revival across North Africa since the Arab Spring upheaval of 2011, is as strong as ever in Morocco.

While the largely peaceful "traditional" branch of the movement commands the biggest following here, the more radical Salafi jihadists are active too.

In the months after mass demonstrations swept Morocco's main cities in early 2011, the king freed scores of Muslims extremists jailed in connection with the Casablanca bombings, among them four radical Salafist leaders.

In a sign that the hardline religious current is taking hold, the niqab, or full women's face veil, is increasingly visible in Morocco's main cities, where 10 years ago it was virtually non-existent.

For Abdullah Rami, an expert on Islamist movements, Morocco's firebrand Salafist clerics benefit from the fact that their ideas are easy to understand and have a receptive audience among the country's poor.

"They aren't a threat to the Moroccan state, which is strong. But they do have a radical ideology that could mobilise people to carry out attacks," he said.

"They refer to the wars in the Arab world, in Syria, in Iraq, in Somalia, and that helps them."

Rights activists and family members say hundreds of Islamists who have committed no crimes and have never supported any jihadist ideology remain behind bars.

Hassan Kettani, one of the hardline clerics freed in 2012, after being jailed for 20 years in connection with the Casablanca bombings, insists he does not support violence.

But, speaking to AFP, he questioned why jihadist fighters should not assist the armed rebels in Syria.

"If someone supports those guys fighting Bashar al-Assad, why if he's an Islamist does he have to be put in jail, but if he's an atheist or a communist or anything else, no problem about him?"