Two teenage French girls, arrested last week in a crackdown on citizens who consider traveling to other countries to join “jihad,” were planning to attack a synagogue in Lyon with a suicide bomb, French media revealed Friday.

The two, 15 and 17 years old, were detained and interrogated last week in Venissieux, a suburb of Lyon in southeastern France, and Tarbes, a town in the south, after French authorities uncovered a plan to bomb the Great Synagogue of Lyon. They were charged for conspiracy to commit terrorism.

The two had never met but communicated via social media, the investigation revealed.

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“These girls were part of a network of young Islamists who were being monitored by security services,” an unnamed security source was quoted by Newsweek as saying.

They’re neither the first adolescents nor the first females arrested in France. Some after returning from Syria or fetched by families at the Turkish border.

The girls are among some 60 people being investigated in France for criminal association in relation with a terrorist enterprise, in one example of how France is taking judicial action against citizens suspected of seeking careers as foreign fighters, even if they have yet to leave French soil. Thousands of European citizens have made the trip to Syrian battlegrounds, but there is no unified plan of action in Europe.

France is leading the way in Europe in the battle against this problem, and its sweep could get even wider with a planned law that would allow passports to be confiscated from those suspected of planning to fight in Syria or Iraq, and would create new measures to prosecute jihadi wannabes or returnees. France also is planning to join other European countries in blocking Internet sites that espouse the jihadi cause.

All of Europe is worried about the return of battle-hardened citizens looking to continue their jihad in their homeland.

The concern has grown acute with the beheading of American journalist James Foley — by an executioner with an English accent. The group calling itself the Islamic State — now regarded by Western authorities as the most brutal among jihadi organizations — claimed responsibility last week by posting a video of the slaying on the Internet.

France also points to the suspected killer of four people at the Jewish Museum in Brussels in May, Frenchman Mehdi Nemmouche, who fought in Syria, as evidence of the need to prevent potential catastrophes.

“Must I wait for a new Mehdi Nemmouche to fire before I act?” Interior Minister Bernard Cazeneuve said in a recent interview with the online publication Mediapart. He was referring to the tough new measures to be debated this fall — and contending they will not compromise civil liberties.

France, with a Muslim population estimated at 5 million — the largest in Western Europe — is particularly concerned about the flight of youths to the battlefields.

French authorities say there are some 900 people from France who have been implicated in jihad — meaning they have taken part in one, plan to join one, or are returning from one. Several dozen have been killed.

Such measures would put France ahead of other countries in its effort to stop the problem, which some experts see as getting worse.