Vandals defaced the walls of a mosque in western France with Islamophobic graffiti, two days before the expected start of Ramadan, local officials said on Sunday.
Interior Minister Gerald Darmanin condemned the incident, which comes just days after an attack on another mosque in western France and as Muslims say hostility towards their community is increasing.
A caretaker and members of the local Muslim community in the city of Rennes discovered the graffiti early on Sunday on the walls of the mosque and Islamic cultural centre.
They included tags insulting Islam and the Prophet Mohammed, and a call for Catholicism to be made the state religion.
The prosecutor's office in Rennes has opened an investigation.
Mohammed Zaidouni, president of the local regional council of Muslims, condemned the "obscene phrases".
"We are the children of the pepublic and we find ourselves facing hate, violence and barbarism," Mr Zaidouni told AFP.
Mr Darmanin tweeted a message of solidarity on Sunday, and said he would visit the mosque later in the day.
The socialist Mayor of Rennes, Nathalie Appere, and its senator, Valerie Boyer, of the right-wing Republicans, both denounced the incident.
In the western city of Nantes, the door of a mosque was destroyed by fire on Thursday night.
And on Friday, a neo-Nazi, 24, was charged for making threats against a mosque in Le Mans, also in western France.
Abdallah Zekri, president of the National Observatory Against Islamophobia, denounced what he said was the anti-Islam climate in France.
"Unfortunately, the declarations of certain politicians are only making things worse," Mr Zekri said.