Rail traffic in and around the western German city of Duisburg faced significant disruptions on Thursday after a fire broke out in a cable tunnel, in what authorities suspect was an act of sabotage, police said.

Investigators ruled out accidental causes and said the state security division was investigating the incident "in all directions." No injuries were reported.

According to the daily newspaper Bild, citing news agency DPA, an ignition device was allegedly placed in the tunnel, causing damage to about 60 meters of cable that will need replacement.