Construction of the mosque in the small town of Bergerac — known for its fine Bordeaux wines and for its association with literary figure Cyrano de Bergerac — has been contested since it was first proposed in 2017 and finally approved in October 2018, despite widespread local opposition.
"The perpetrators smeared the walls with animal blood and placed a severed pig's head" on the front gate of the construction area, the deputy public prosecutor of Bergerac, Charles Charollois, told AFP.
The vandalism took place overnight and wasn't discovered until workers arrived in the morning.
"This building project is controversial," Charollois said.
"There have been administrative and legal appeals to stop it, so there are many leads for us to follow."
Bergerac's police commissioner, Frederic Perissat, "strongly denounced and condemned these acts that damage our freedom of conscience and expression and are contrary to the principles of separation of church and state," and called for "mutual respect" in the community.