The Grand Synagogue of Marseille. Photo: WikiCommons.

French police are guarding ninety synagogues and Jewish schools in Marseille after the shooting attack at the Jewish Museum in Brussels killed four people last month, the UK Guardian reported on Wednesday.

Michèle Teboul, the leader of a regional Jewish organisation, was quoted as saying that Marseilles’s 80,000-member Jewish community had no alternative other than to “bunkerize.” The city has 850,000 people, a quarter of whom are Muslim.

The lead suspect in the Brussels attack, Mehdi Nemmouche, was arrested on May 30 at the Marseille bus station, but fear pervades the city, with the adjacent Saint-Charles train station evacuated during rush-hour last Friday after the discovery of a suspicious package.

The Guardian said the arrest of Nemmouche has focused police attention on the estimated 780 French jihadists returning from the war in Syria, Nemmouche is suspected of carrying out the attack after returning from Syria via a circuitous route through Asia.

French Prime Minister Manuel Valls, who had been Interior Minister until last month, said the threat of the returning jihadists was “without a doubt, the greatest danger that we must face in the coming years.”

Deputy Mayor of Marseille Nora Preziosi said, “The vast majority of Muslims are republican, they are against what is happening. Islam is being sullied by the Salafists, and stigmatized by the media.”

Referring to Nemmouche, she added: “What was he doing in Marseille? He should have been followed. These people should be placed under surveillance, that’s the state’s responsibility.”

Camille Hennetier, a deputy prosecutor in charge of the central investigative anti-terrorist unit in Paris, said, “It’s not a crime to be radical… But it is a crime to wage jihad.”

So far, French police have arrested 21 people over the past 18 months who they linked to a group with Syria connections known as the “Cannes-Torcy” cell. Six alleged jihadist recruiters were also detained last week after Nemmouche’s arrest.

Compared to the conflict in Afghanistan, when 90 violent extremists returned to France, French Interior Minister Bernard Cazeneuve said 285 French jihadist fighters are now in Syria, up 75 per cent from six months ago. French President François Hollande said last week that 30 French nationals had been killed in the Syrian civil war.