French prosecutors said they had opened an investigation into possible arson after fire damaged a cathedral in the city of Nantes on Saturday, noting the blaze had erupted in three separate places.
"An arson investigation has been opened, there are no conclusions to be drawn now because we have a lot of investigations to make which could introduce new elements," Nantes prosecutor Pierre Sennes told AFP.
The fire erupted on Saturday morning inside the gothic cathedral in the western city, destroying the organ, but firefighters brought the blaze under control within hours.
"When we arrive at a place where a fire has taken place, when you see three separate fire outbreaks, it's a question of common sense, you open an investigation," Sennes said.
"We cannot leave an event like that without a judicial investigation."
He said federal police were now involved and an expert on fires from the police technical and scientific unit was travelling to Nantes to join the investigation.
Sennes said there were no suspects in the probe at the moment.