France has thwarted five terror attacks and dismantled 13 networks linked to extremists in Syria but the number of young people leaving to join the fight has doubled in the past year, the country’s top security official said Wednesday.

French fighters make up the largest contingent of Europeans being recruited to join Muslim extremists in Iraq and Syria, and security officials fear they will return newly skilled in warfare and carry out attacks at home.

Calls by the Islamic State group for lone-wolf attacks in the West have heightened anxiety. A Frenchman who is believed to have fought with the organization is charged in a deadly shooting at a Brussels Jewish museum.

Interior Minister Bernard Cazeneuve said Wednesday that France was committed to stopping the networks, but said about 1,200 citizens have left for Syria, including about 400 still in the war zone and 200 on their way.

He gave no details on the five attacks he said had been stopped since August 2013, beyond saying they were planned either by recent returnees from Syria or those who had not yet left for the war zone.

Two young women accompanied by two children were blocked at the Paris airport on Saturday en route to Turkey, Cazeneuve said in a report to the government. But many leave unimpeded, especially young people who hide their intentions to family and friends.

About a third of would-be jihadis are recent converts to Islam, Cazeneuve said.

(AP)