A judge has handed a 16-year-old French girl preliminary terrorism charges for allegedly supporting the Islamic State group and trying to perpetrate an attack, prosecutors have said.

The girl was using a social media app to spread calls by Isis to commit violent acts, the Paris prosecutor’s office said on Monday.

The judge charged the teenager with taking part in a “criminal terrorist association” and “inciting to commit terrorist acts through an online communication medium”. She has been placed in custody.

The investigators said the girl was “extremely radicalised” and was the administrator of a chat group dedicated to Isis propaganda on the Telegram app, which has been used by suspected jihadis to communicate, deputy prosecutor Laure Vermeersch said. Vermeersch said no specific targets had been mentioned by the teenager, who had no prior criminal history. Her name wasn’t released.

Investigators are now trying to trace other participants of the chat group and know whether the girl had possible accomplices in her alleged attack plot or in spreading Isis propaganda.

The girl was arrested on Thursday in the Melun region, a southern Paris suburb, during a police operation. It is not the first time a girl has been detained in France under suspicion of trying to commit an attack. In March, two girls aged 15 and 17 were charged with taking part in a criminal terrorist association for allegedly plotting to attack a target – possibly a Paris concert hall – in a copycat action of November’s Bataclan attack in the capital. But investigators acknowledged the plot was not in an advanced stage.

France has lived under a state of emergency for nearly nine months, since the deadly attacks in November in Paris that killed 130 people. Parliament has extended the measure for six more months after a truck attack in the southern city of Nice on Bastille Day (14 July) that killed 85 people and was claimed by Isis.