Police and justice sources meanwhile said four people had been arrested in and around Montpellier, southern France, on suspicion of planning an attack.
The teenaged girl had used social media to try to find ways of travelling to Syria to join up with jihadists, the same source said.
The announcement came a week after a soldier shot a man wielding a machete near the Louvre museum in Paris.
Two of the four arrested were a 16-year-old girl and a young man that had already been under surveillance for ties to radical Islamists.
France has been repeatedly targeted by Isis, whose militants launched a series of mass shootings and suicide bombings across Paris that killed 130 people in November 2015.
The four arrested are suspected of plotting an imminent attack, Reuters news agency quoted the interior ministry as saying. Police also found more ingredients that could have been used to produce more of the explosive.
Over the past two years, France has suffered a string of bloody attacks by Islamic extremists that has claimed more than 200 lives.
According to several reports out Friday, a 10-member constitutional council vetoed the law because it said it unnecessarily violated the people's freedom of communication. While praising the security personnel for making the arrests, Roux said three among the arrested were directly suspected of preparing a violent attack against the country.