A knife attack early on Saturday in the Gare de Lyon rail station in Paris left three people wounded, police said, ruling out terrorism at this stage.
Police arrested the suspected attacker, who showed signs of mental disorders, Paris police chief Laurent Nunes told reporters. "We found medicine on him which suggests he was undergoing treatment."
Two of the victims suffered light wounds while the third was more seriously hurt but was not in a life-threatening situation, police said.
The attacker, who carried Italian residence permits and was in France legally, attacked travelers with a knife and hammer. French media said he was originally from Mali, but Nunes did not confirm the reports.
France has suffered a series of Islamist militant attacks over the past decade, but also occasional assaults by mentally ill people.