Riot police have been patrolling suburbs west of Paris that have seen cars torched and a police station attacked amid tensions linked to authorities' handling of France's ban on Muslim face veils.
Some 20 cars were set ablaze overnight and four people were detained in a second night of violence, officials said. Interior Minister Manuel Valls said the overnight incidents targeted the town of Elancourt.
The second night of unrest seemed less intense and appeared to involve fewer people than the night before, when some 250 people clashed with police in the nearby town of Trappes. But the interior minister insisted in a statement that extra police will remain deployed in the area and stay as long as needed until calm returns.
The violence evoked memories of weeks of trouble in neglected neighbourhoods around France in 2005. That was sparked by the deaths of two teenagers who were electrocuted while hiding from police, as people around the country - many of them jobless youths from poor, immigrant backgrounds - unleashed pent-up frustrations on police and public property. While the government has poured money into projects to solve some of the problems that led to that rioting, tensions remain.
The violence began on Friday after a group of residents gathered at the police station to protest the arrest of a man whose wife was ticketed for wearing a face veil. The regional prosecutor said the husband tried to strangle the officer who was doing the ticketing.
France has barred face veils since 2011. Proponents of the ban argue the veil oppresses women and contradicts France's principles of secularism, which are enshrined in the constitution. The ban affects only a very small minority of French Muslims, but some say it feeds discrimination against moderate Muslims too.
On the first night of unrest in Trappes, a 14-year-old boy and three police officers were injured and several people detained.
David Callu of the SGP police union said of the second night: "The beginning of the night was calm, nothing happened. But in the second part of the night, a small group formed. About 50 assailants were involved, they started to fight against police and burned vehicles and garbage and public goods."
He said some assailants were firing weapons and a gasoline bomb at police. Meanwhile, a warehouse of house and garden materials is ablaze in Trappes and authorities are trying to determine whether there is a link to the other violence.
Benoit Hamon, the government's minister for social and economic solidarity, said: "We will be severe against those who attack public goods but also against those who do racist and Islamophobic acts."