Youths in the southeastern French town of Firminy burned cars and destroyed a social centre overnight on Wednesday as protests over the death in police custody of a young man continued for a second night.
Around 200 riot police were deployed to control the situation with a helicopter circling overhead as groups of young people set fire to rubbish bins before moving on to torch cars and the social centre.
The protests followed the death on Wednesday of Mohamed Benmouna, a local man arrested for attempted extortion, who fell into a coma after what police said was a suicide attempt and died several hours later.
Benmouna's family have expressed scepticism over the explanation by police who said he had used cords from a mattress to hang himself.
The state prosecutor in Saint-Etienne, the nearest major city, rejected suggestions of police abuse but said video surveillance equipment that would normally have filmed Benmouna's cell was not functioning properly.
An autopsy has been ordered and an inquiry into the case opened by the IGPN, the police inspectorate.
Nine people were arrested on Wednesday after a night of violence on Tuesday evening when Benmouna was still alive but in a coma following the incident.