French PM Dominique de Villepin has pledged to toughen anti-vandalism laws after a woman was severely burnt in an arson attack on a bus in Marseille.
The bus attacks have fuelled fears of a new wave of rioting
Existing laws would be broadened to punish all those who are "involved in and encourage" such attacks, not just the perpetrators, Mr de Villepin said.
The Marseille attack left a 26-year-old woman with burns to most of her body.
France has seen a recent rise in such attacks, a year after a wave of rioting rocked its impoverished suburbs.
Gangs of youths, many of them of immigrant descent, torched cars and clashed with police during three weeks of unrest last year.
Earlier on Monday, the French government held an emergency meeting on transport security.
Mr de Villepin appealed for witnesses to the Marseille attack and Interior Minister Nicolas Sarkozy said the perpetrators would be tracked down and punished. About 200 extra police were deployed in the city.
A group of teenagers reportedly forced open the doors of the bus vehicle and threw a flammable liquid inside before fleeing.
A 26-year-old French woman of Senegalese origin was unable to escape and suffered burns to 70% of her body.
About 200 vehicles were set alight in incidents around the country on Saturday, and nearly 50 people were arrested.
French news agency AFP said youths in Grenoble threw a stone from a bridge onto a tram, smashing the window and injuring the driver.
Last year's riots were sparked by the deaths of two teenagers in a suburb of Paris. There is dispute over whether they were chased by police before they were electrocuted while hiding in an electricity sub-station.
During the violence last year, more than 10,000 cars were set ablaze and 300 buildings firebombed.
Community leaders in run-down French suburbs have warned that the factors which played a key part in the riots - high unemployment, racial discrimination and alienation from mainstream society - remain unchanged.