A man driving a van ploughed into a crowds at a Christmas market in Nantes, western France, injuring 10 people.
Five people suffered serious injuries, including the driver, a police official told Reuters.
According to local newspaper Ouest France, citing a police officer and witnesses on the scene, the driver of the white van shouted "Allahu Akbar" ("God is greatest" in Arabic) and then stabbed himself with a knife.
The Christmas market was evacuated and secured by police, a Reuters witness reported.
The incident comes only a day after pedestrians were run down in Dijon.
The driver of the vehicle screamed "God is great" in Arabic.
On Sunday, a man police in Tours shot dead after he attacked them had used the same phrase.