French police arrested four people suspected of recruiting militants to fight for Islamist networks in Syria, officials said Monday.

The arrests follow the detention of a 29-year-old Frenchman named Mehdi Nemmouche who was arrested at a station in Marseille on Friday, according to prosecutors, for killing three people at Brussels' Jewish Museum on May 24, and spending more than a year fighting with Islamist insurgents in Syria, Reuters reported.

“There are people who recruit jihadists. There are as I'm speaking arrests being made,” Bernard Cazeneuve, France’s interior minister, told French radio station Europe 1, referring to the arrests that took place in the Paris region and in the south of France. “We are acting everywhere. There will be no respite in the fight against terrorists.”

Although there is no suggestion of a link between Monday’s arrests and the detention of Nemmouche during a random check on Friday, the latter is believed to have had connections with radical Islamists. Nemmouche also had served five years in jail in France for robbery before he was released in December 2012, BBC reported.

Following Monday’s arrests, European governments also raised concerns that citizens with a Muslim immigrant background, who go to fight in Syria's civil war, may import Islamist militancy upon their return.

The Nemmouche episode showed “the stupifying naivety of the government,” Marine Le Pen, president of the far-right National Front party, which won in the country's European elections last week, told Reuters. “We must put a stop to this mass immigration.”

Meanwhile, Roger Cukierman, head of France's CRIF Jewish association, urged for more resources to be made available to the Direction Générale de la Sécurité Extérieure, or DGSE, to track militants returning to France from Syria.

“The DGSE (external intelligence service) should probably get more resources to be able to follow the tracks of these people very closely,” Cukierman told France’s RTL radio.