The attack is just the latest in a string of attacks on Muslim places of worship over the past ten years.
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, told French news agency 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.
Over the past few days, posters declaring "Bergerac is the city of Perigord, not Islam!" -- referring to the former name of the Dordogne region -- had been pasted around the town, according to its mayor Daniel Garrigue.
"I can't say that they're connected, but I note that they're in the same spirit," Garrigue said. In France, desecrating a religious facility is a crime punishable by up to seven years in prison.
The attack on the site in Bergerac comes less than two weeks after a gunman killed 50 Muslims in Christchurch, New Zealand, and injured another 50, during a shooting spree at two mosques.
Its not just mosques that have been targeted. Earlier this year, 80 graves were vandalised at a Jewish cemetery in eastern France, local officials said Tuesday, on the eve of nationwide marches against a rise in anti-Semitic attacks.
The damage was discovered at a cemetery in the village of Quatzenheim, close to the border with Germany in the Alsace region, a statement from the regional security office said at the time.
Photos show the Nazi symbols in blue paint spray-painted on the damaged graves, one of which bears the words "Elsassisches Schwarzen Wolfe" ("Black Alsacian Wolves), a separatist group with links to neo-Nazis in the 1970s.