A small bomb exploded overnight near the arena where the medieval French town of Carcassonne is preparing to stage its first bullfight in 50 years today, police said.
The homemade device caused no damage.
No group claimed responsibility for the attack and the bullight, which has unleashed protests from animal welfare activists including former film star Brigitte Bardot, will start as planned this afternoon.
Animal welfare campaigners plan to stage a peaceful protest in Carcassonne to coincide with the event.
On Friday, a local civil court overruled objections from campaigners seeking to halt the Spanish-style bullfight, the first in the southwestern town since 1954.
Two separate animal welfare groups had filed a suit seeking to block the bullfight on the grounds that it was not a local custom. They have appealed against Friday's ruling.
While torturing animals is illegal under French law, bullfights, or corridas, are permitted in areas that have an unbroken local tradition of ritually slaughtering bulls.
Mr Raymond Chesa, the mayor of Carcassonne, has defended his decision to authorise the planned novillada, a fight involving young bulls, on the grounds that the area has a strong Spanish immigrant tradition.