France's interior minister revealed Thursday that hundreds of homegrown militants were signing up to fight in Syria and warned they could pose a security threat when they come back.
More than 300 French nationals or residents are either currently fighting in Syria's civil war, planning to go and fight or have recently returned from there, the minister, Manuel Valls, told France Inter radio.
Most of them were young men, often with a delinquent past, who had become radicalised, he said.
"This is a phenomenon which worries me because they represent a potential danger when they return to our soil," Valls said. "We have to be extremely attentive."
France, which has the largest sectarian population in western Europe, has increased its monitoring of radicals since Al-Qaeda-inspired gunman Mohamed Merah killed seven people in and around the southwestern city of Toulouse last year.
It subsequently emerged that Merah had spent time in Pakistan and Afghanistan and that French intelligence had been aware of his contacts with militants in those two countries.
According to British defence consultancy IHS Jane's, there are up to 10,000 jihadists from all over the world currently fighting in Syria on the side of rebels trying to overthrow President Bashar al-Assad, whose regime they want to replace.