Two people were also detained over the rioting on the French Mediterranean island, which saw rioters vandalise a Muslim prayer hall and set fire to books including copies of the Koran.
Corsica's administrator Christophe Mirmand announced a ban on all protests and gatherings until at least January 4 in the poor Jardins de l'Empereur housing estate, the epicentre of the violence.
The ban came after hundreds of people had marched for a second straight day Saturday through several working-class districts of Ajaccio shouting slogans such as “This is our home!” and “Arabs get out”. Two men aged in their 20s were held in custody as part of the probe into the unrest.
Defying the ban, about 300 people were massed on Sunday at the entrance to the estate in a standoff with police, an AFP journalist said.
The unrest followed a Christmas Eve clash in which two firefighters and a police officer were injured at the estate, home to some 1,700 people, half of them of non-French origin.
Regional official Francois Lalanne said a fire had been deliberately lit in the neighbourhood in a ruse aimed at “ambushing” the emergency services.
A firefighter told French television that “about 20 people armed with iron bars (and) baseball bats” had tried to attack them but were unable to smash through the windows of their truck.
The next day, 600 people gathered outside police headquarters in Ajaccio in a show of support for the police and firefighters. But some 300 broke away to head for the housing estate.
Shouting xenophobic slogans, the group smashed a Muslim prayer room, partially burning books including copies of the Koran, Lalanne said.
French Prime Minister Manuel Valls wrote on Twitter that the break-in was “an unacceptable desecration”, while also condemning the “intolerable attack” on the firefighters.
“This behaviour must stop. It hurts Corsica's image,” Mirmand said, describing as “shocking and unacceptable” remarks that could lead to prosecution for hate speech.
The unrest came as France remains jittery following the November 13 jihadist attacks in Paris that left 130 dead.
Regional elections in mid-December handed major gains to France's anti-immigration far right, with Corsica's nationalist party winning power for the first time.
The population of France's lush Mediterranean “Isle de Beaute” (Island of Beauty) increases by tenfold during the peak tourist season.