Updated

France's interior minister sent riot police to patrol the southern port city of Marseille on Sunday after a group of marauding teenagers torched a bus, gravely burning a young woman.

French police braced for violence this weekend, the anniversary of last year's riots in poor neighborhoods where immigrants from former French colonies in Africa live with their French-born children on the fringes of society.

On Saturday, 46 people were taken into custody, most of them in the communities around Paris, and two police officers were slightly injured. The most serious violence was the brutal bus attack in Marseille.

A group of young people burst onto the bus and tossed in a bottle of flammable liquid before fleeing, police said, citing witnesses' accounts. The resulting fire injured a 26-year-old woman, who suffered second- and third-degree burns on her arms, legs and face and was in a medically induced coma on Sunday.

President Jacques Chirac telephoned the woman's family, ensuring them that France would "do everything to find the assailants and punish them with the greatest severity," his office said.

Prime Minister Dominique de Villepin called a meeting for Monday on public transport safety, while Interior Minister Nicolas Sarkozy's office said he was sending two extra companies of riot police to Marseille. Bus drivers in Marseille refused to return to work.

Though youths have burned other buses during flare-up of violence, passengers have generally escaped before the vehicles went up in flames. Another bus was burned Saturday in Trappes, outside Paris, but its passengers fled unharmed, police said.

The three weeks of rioting last year were fueled by anger at France's failure to offer equal chances to many minorities, including France's 5 million-strong Muslim population.

The rioting was sparked by the deaths of two teenagers who were electrocuted in a power substation in Clichy-sous-Bois on Oct. 27, 2005, where they were hiding after what they thought was a police chase.

For the anniversary of the teens' deaths, national police said about 4,000 extra police and riot officers were deployed across the country to cope with a possible resurgence of violence. Some 7,000 police are at the ready on an average night in France.

Aside from the bus attack in Marseille, the Interior Ministry said that both Friday and Saturday night were "relatively calm." Youths set fire to about 200 vehicles Saturday, police said. But even on ordinary nights, the number of cars burned often reaches 100.

France's trouble integrating minorities and the unrest in poor neighborhoods have become political priorities in the campaign for next year's presidential and parliamentary elections.

The government passed an equal opportunities law this spring and has poured in funds to its "sensitive" areas, but disenchantment continues.