PARIS —  French President Jacques Chirac (search), intervening after six nights of rioting in housing projects outside Paris, called Wednesday for calm and said authorities will use a firm hand to curtail what may become a "dangerous situation."

The violence, sparked initially by the deaths of two Arab teenagers, has exposed the despair, anger and deep-rooted criminality in poor suburbs, where police hesitate to venture and which have proved fertile terrain for Islamic extremists.

"The law must be applied firmly and in a spirit of dialogue and respect," Chirac said at a Cabinet meeting. "The absence of dialogue and an escalation of a lack of respect will lead to a dangerous situation."

Chirac's remarks were passed on to reporters by government spokesman Jean-Francois Cope.

The rioting, which spread Tuesday night to at least nine Paris-region towns, has exposed rifts in Chirac's government, with Interior Minister Nicolas Sarkozy — a potential 2007 presidential candidate — being criticized for his tough talk and police tactics.

It also has renewed debate about France's failure to fully integrate its millions of immigrants, many of whom are trapped in poverty and grinding unemployment, living in low-cost, sometimes decrepit, suburban housing projects where gangs dealing drugs and stolen goods sometimes are in control.

That Chirac intervened personally was a measure of the crisis. He acknowledged the "profound frustrations" of troubled neighborhoods but said violence was not the answer and that efforts must be stepped up to combat it.

"Zones without law cannot exist in the republic," the French leader said.

In Tuesday night's clashes, riot police fired rubber bullets at advancing gangs of Muslim youths in Aulnay-sous-Bois (search), where 15 cars were burned, officials said. Youths lobbed Molotov cocktails at an annex to the town hall and threw stones at the firehouse. It was not immediately clear whether there were any injuries.

Interior Minister Nicolas Sarkozy (search) told Europe-1 radio that police detained 34 people overnight.

Sarkozy — blamed by many for fanning the violence with his "zero-tolerance" approach to suburban crime — defended his approach and vowed to restore calm. He recently called rioters "scum" and vowed to "clean out" troubled suburbs.

Housing projects to the north and northeast of Paris are heavily populated by North African Muslim immigrants.

Because of the unrest, Prime Minister Dominique de Villepin (search) delayed a three-day visit to Canada due to start Wednesday, and Sarkozy canceled a visit to Pakistan and Afghanistan planned to begin Sunday.

In unrest Tuesday night, rioters burned 228 cars throughout France, police said. Some 153 of those were in the Seine-Saint-Denis (search) area north of Paris, where the rioting began.

The rioting began Thursday in the northeastern suburb of Clichy-sous-Bois (search) after the electrocutions of two teenagers hiding in a power substation because they believed police were chasing them.

Officials have said police were not pursuing the boys, aged 17 and 15.

Villepin met Tuesday evening with the parents of the three families, promising a full investigation of the deaths and insisting on "the need to restore calm."

There was a heavy police presence in Clichy-sous-Bois, which had its first calm night Tuesday since the riots began. Mayor Claude Dilain said it was "not yet a victory, because we all have the feeling that this calm could be precarious."

"If French society accepts that there are tinderboxes within its borders, it can't be surprised when they explode," he said.

In the northeastern suburb of Bondy (search), 14 cars were burned and four people arrested for throwing stones at police, authorities said.