"It is contemptible," Hajii Mohamed, the mosque’s imam, told Agence France-Presse (AFP).
"To attack a religion like this, I don't know what is happening. People lose their heads, especially during Ramadan."
Two pig heads were hung Wednesday, August 1, on a gate at the entrance of the mosque in the southern city of Montauban shortly before Fajr prayers.
A large amount of pig blood was spilled on the ground.
Islam considers pigs unclean because they are omnivorous, not discerning between meat or vegetation in their natural dietary habits unlike cows and sheep for instance, which eat only plants.
Muslims do not eat pork and consider pigs and their meat filthy and unhealthy to eat.
The umbrella French Council of the Muslim Faith described the defilement of the mosque as "a racist and xenophobic provocation".
It called on French authorities to bring those responsible to justice swiftly.
The town of Montauban saw the killing of two French paratroopers by a self-styled Al-Qaeda gunman in March.
The gunman was killed in a police siege of his apartment after killing five people, including three Jewish children.
The incident was the first in the southern Tarn-et-Garonne region, leading to speculation it was a response to the March shooting spree.
Muslim leaders have distanced their faith from the shooting, saying it was against the teachings of Islam.