While no details on the pair have been released, French anti-terrorist investigators have expressed increased concern over the young age of some suspects detained in recent months for planning militant attacks.

The 19-year-old has been charged with “terrorist conspiracy” to commit attacks and the “acquisition and possession of arms for a terrorist enterprise,” said the judicial source, speaking on condition of anonymity.

The youth aged under 18 was detained on June 13, the source said.

The pair made contact on social media and were planning a “violent action notably aiming at Jewish targets,” said the source without giving details on the plot.

Anti-terrorism investigators say a growing number of youths have been held in recent months for preparing attacks.

“This is a necessarily worrying phenomenon,” senior anti-terrorist prosecutor Olivier Christen said at an evidentiary hearing on Wednesday.

French politicians have also condemned a growing number of attacks on the country’s Jewish community, the biggest outside Israel and the US.

Outrage has been expressed over the rape of a 12-year-old Jewish girl in a park in the Paris suburbs last Saturday. Two 13-year-old boys have been charged with rape and making antisemitic insults.

Several protest rallies have been held in Paris and other French cities over the case which comes as France prepares for a national election in which the far-right National Rally party is tipped to make major gains.