A thousand police officers are being deployed in the suburbs of Paris, after seven consecutive nights of rioting.
The officers will be stationed in Seine-Saint-Denis, north-east of Paris. Half of the department's 40 towns were affected by violence last night.
Prime Minister Dominique de Villepin has been holding emergency crisis talks, following criticism at his failure to end the violence.
So far, police on Thursday night have reported a small number of incidents.
In Seine-Saint-Denis, a number of cars were set alight, projectiles were thrown at police and fires were reported in two towns.
The unrest has also spread beyond the Paris region for the first time, with reports of cars on fire in the central town of Dijon.
The riots were triggered by the deaths last week of two teenagers of African origin.
Bouna Traore, aged 15, and Zyed Benna, 17, were accidentally electrocuted at an electricity sub-station in Clichy-sous-Bois. Local people say they were fleeing police, a claim the authorities deny.
A criminal investigation and an internal police inquiry have been opened.
Mr de Villepin said restoring order was his "absolute priority".
In scenes of escalating unrest overnight on Wednesday, shots were fired at police and firefighters, while gangs besieged a police station, set fire to a car showroom and threw petrol bombs. At least 177 cars were also set alight.
On Thursday night, 1,000 police will be stationed near car showrooms, shopping centres and government buildings in Seine-Saint-Denis.
Interior Minister Nicolas Sarkozy, who earlier met the dead teenagers' families, said the violence was "not spontaneous" but rather "well organised".
He said the government would not allow "troublemakers, a bunch of hoodlums, think they can do whatever they want".
On Thursday afternoon, Mr de Villepin held cross-party crisis talks with Mr Sarkozy, other ministers, MPs and mayors of the some of affected towns.
Mr de Villepin and Mr Sarkozy and are likely rivals for the presidency in 2007, and their different approaches to the rioting had split the cabinet.
Mr Sarkozy has caused controversy with his strong language, labelling the rioters as "rabble" and saying many of the suburbs need "industrial cleaning". Mr de Villepin has preached a more conciliatory message, urging ministers not to "stigmatise" vast areas.
Francois Masanet, secretary general of the French police union, described the situation as "dramatic", and warned that the violence could escalate.
The areas affected are poor, largely immigrant communities with high levels of unemployment.
Many youths in the suburbs feel alienated from French society
Minister for Social Cohesion Jean-Louis Borloo said the government had to react "firmly", but added that France must also acknowledge its failure to deal with anger simmering in poor suburbs for decades.
Ruling UMP MP Jacques Myard said the violence was a failure of the French model of integration, but that the government had been weak.
It had "accepted, step-by-step, that every night youths burn cars, destroy business and so on. Those guys will use the pretext of everything to riot, to demonstrate, to destroy", he said.
Muslim leaders have urged politicians to show respect for immigrant communities.
Dalil Boubakeur, the head of the Paris mosque and the president of the French Council for the Muslim Religion, said Muslim immigrants in the suburbs "must be given the conditions to live with dignity as human beings", not in "disgraceful squats".
Clichy-sous-Bois: Two teenagers die in electricity sub-station on 27 October. Successive nights of rioting follow rumours they were fleeing by police. A number of people arrested or injured.
Aulnay-sous-Bois: A flashpoint after violence spread from Clichy. Shots fired at police and cars and shops set ablaze. Further trouble in eight nearby suburbs, with more shots fired at police.
Others: Police report incidents involving gangs of youths in town in the suburban departments of the Val-d'Oise, Seine-et-Marne and Yvelines. Reports of petrol bombs thrown at a police station in the Hauts-de-Seine.