Spokeswoman Frederique Olivaux said a homemade bomb went off today around 4 am in front of the building in Corsica's second city, Bastia.
It shattered the windows and damaged the door, but Olivaux said no one was injured.
She added that a police investigation has been opened - and since no person or group has claimed responsibility, all options are being explored.
Corsica is home to an active separatist movement and has a history of mafia gang violence.
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