French President Nicolas Sarkozy is holding emergency talks with ministers to discuss a wave of urban violence.
Mr Sarkozy vowed to punish those who shot at police
More than 120 police were injured in two nights of unrest, after two teenagers died on Sunday when their motorbike and a police car collided.
Tuesday night passed more calmly, with isolated clashes in Paris and Toulouse, as police reinforcements were deployed.
Mr Sarkozy, returning from a visit to China, said those who shot at officers would be brought before the courts.
Visiting policemen injured in the riots, he said: "Opening fire at officials is completely unacceptable," calling it a crime that "has a name, it is attempted murder".
Mr Sarkozy also met the families of the two teenagers and said he was opening a judicial inquiry into the deaths, a lawyer for the relatives told AFP news agency.
The lawyer, Jean-Pierre Mignard, welcomed the move, saying it would allow the families and their representatives "to participate actively in the search for the truth".
Prime Minister Francois Fillon, Interior Minister Michele Alliot-Marie and other senior members of the government have joined Mr Sarkozy for the crisis talks.
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"The government will do all it can to ensure that order returns as soon as possible," Mr Fillon said earlier.
"The situation is much calmer than the two previous nights but we can all feel that it remains fragile," he said, after Tuesday night saw only minor incidents in Villiers-le-Bel, the northern Parisian suburb which had seen two nights of serious rioting.
But for the first time the violence spread to other cities, with at least 10 cars burnt and a fire at a library in Toulouse.
The violence is more intense than during weeks of clashes in the French suburbs in 2005, due to the more frequent use of firearms by rioters, police unions have said.
Relatives of the two dead teenagers, who were both of North African descent, have insisted that police rammed their motorcycle before leaving them to die.
But the initial findings of an internal police probe, which found that police were not to blame, sparked anger in Villiers-le-Bel.
Police say the motorcycle was going at top speed and was not registered for street use, while the two boys - who have been named only as Moushin, 15, and Larami, 16 - were not wearing helmets and had been ignoring traffic rules.
Mr Fillon, who visited the scene on Tuesday, called the rioters "criminals" and said nothing could justify the attacks.
Security was stepped up in Paris for Tuesday night
Rioting had spread on Monday from Villiers-le-Bel to other areas in the north Paris suburbs.
Ms Alliot-Marie has said the riots were organised and criminals were using youngsters to lure away police while they pillaged shops.
The 2005 unrest, also sparked by the deaths of two youths, spread from a nearby suburb of Paris to other cities and continued for three weeks, during which more than 10,000 cars were set ablaze and 300 buildings firebombed.
Mr Sarkozy was heavily criticised at the time after he called for crime-ridden neighbourhoods to be "cleaned with a power hose" and described violent elements as "gangrene" and "rabble".
The BBC's Alasdair Sandford says that although plenty of money has been poured into areas like Villiers-le-Bel that seems irrelevant when tension and resentment between young people and the police is so strong.