The Paris prosecutor says he will investigate nine people suspected of sabotaging French railways.

Prosecutor Jean-Claude Marin says he will file preliminary charges of "criminal conspiracy in relation with a terrorist enterprise" against the nine suspects. The move gives the judge time to investigate before ordering a trial or dropping the charges.

Police released a 10th suspect on Thursday.

Police say the suspects are believed to have links to far-left and anarchist groups. They were arrested Tuesday after at least six attacks in recent weeks on France's high-speed railways. No one was injured in the attacks, but trains were delayed.

The suspects could face up to 10 years in prison if convicted.