Police arrested five youths Tuesday, aged 15 to 17, suspected of links to the weekend firebombing of a Marseille city bus that left a young woman severely burned, police said.

Meanwhile, the agency that oversees police conduct ordered an investigation into the injury of a 16-year-old during a Saturday night clash with police in Clichy-Sous-Bois, police said Tuesday. The young man was hospitalized with an eye injury, allegedly caused by a flashball, a hard rubber ball, fired by police.

Three weeks of fiery riots that began a year ago last Friday were sparked by the deaths of two youths electrocuted in a power substation while hiding from police in Clichy-Sous-Bois — putting a spotlight on police conduct in the northeast Paris suburb.

Last year's violence spread to neglected housing projects nationwide and laid bare layers of discrimination against citizens of immigrant origin, mostly from former French colonies in African and Muslim North Africa.

In Marseille, police arrested five people in housing projects near the site of the Saturday night bus attack, the most vicious in a series of bus burnings around the Oct. 27 anniversary of the start of the riots.

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Mama Galledou, a 26-year-old student of Senegalese origin, was burned over nearly 70 percent of her body and was fighting for her life, doctors said Monday. She has been kept in an artificial coma.

While car torchings are a nightly occurrence in some rough neighborhoods in France, the brutality of the bus firebombing shocked politicians and the public.

More than a half-dozen buses have been targeted over the past few weeks. Except for the Marseille bus, the attackers first evacuated passengers.

Marseille Prosecutor Jacques Beaume told reporters that the five arrested in the bus firebombing could face criminal charges.

President Jacques Chirac, in an interview published Tuesday in the daily Le Figaro, called for "firmness in the face of violence" along with promotion of equal opportunities for residents of the poor housing projects that ring France's big cities.

This year has not seen a general upsurge in violence like last year's, but isolated incidents persist.

Police clashed Saturday night in one Clichy-Sous-Bois project with about 20 youths who had built a barricade and threw stones at police, police said. Police fired flashballs to disperse the youths, all of whom left the scene except for the 16-year-old, who had fallen to the ground, according to police and judicial sources.

A judicial official said the teen admitted to helping erect the barricade but denied throwing stones at police. The official asked not to be identified because he was not authorized to speak publicly about the incident.

The young man was hospitalized, police said. An investigation was underway. Two officers were slightly injured in the melee and police cars damaged, police said.