French authorities have handed two teenage girls preliminary terrorism charges for allegedly plotting an attack against a Parisian concert hall.

The Paris prosecutor's office said Saturday that the younger girl, who is 15, would remain in custody while her 17-year-old companion would be released under judicial supervision.

They were arrested Wednesday by counterterrorism agents as part of an investigation for criminal conspiracy in connection with a terrorist enterprise.

The investigation comes as France remains under a state of emergency and on high alert after Islamic State-linked extremists attacked the Bataclan concert hall and sites across Paris in November, killing 130.

Prosecutors said early investigations indicate the girls' project appears to have been at an early stage because no weapons or explosives were found.