A plainclothes policeman aims his rifle as he patrols in Villiers-le-Bel, a northern Paris suburb, Tuesday evening. France's government vowed to fight with all its might against armed bands of rioters who rampaged in Paris suburbs, torching cars and buildings and, in a potentially deadly development, firing at police officers. Police reinforcements were sent into the suburbs north of Paris on Tuesday to try to prevent a third night of rioting. The violence was triggered by the deaths of two teens in a crash with a police car Sunday in Villiers-le-Bel.

Villiers-le-Bel, France ? Youths rampaged for a third night in the tough suburbs north of Paris and violence spread to a southern city late Tuesday as police struggled to contain rioters who have burned cars and buildings and – in an ominous turn – shot at officers.

A senior police union official warned that “urban guerrillas” had joined the unrest, saying the violence was worse than during three weeks of rioting that raged around French cities in 2005, when firearms were rarely used.

Bands of young people set more cars on fire in and around Villiers-le-Bel, the Paris suburb where the latest trouble first erupted, and 22 youths were taken into custody, the regional government said. In the southern city of Toulouse, 20 cars were set ablaze, and fires at two libraries were quickly brought under control, police said.

Despite the renewed violence, France’s prime minister said the situation was calmer than the two previous nights. About 1,000 officers patrolled trouble spots in and around Villiers-le-Bel on Tuesday, he said.

The government was striving to keep violence from spreading in what was shaping up as a stern test for new President Nicolas Sarkozy. The unrest showed anger still smolders in France’s poor neighborhoods, where many Arabs, blacks and other minorities live largely isolated from the rest of society.

The trigger was the deaths Sunday of two minority teens when their motorscooter collided with a police car in Villiers-le-Bel, a blue-collar town on Paris’ northern edge.

Residents claimed the officers left without helping the teens. Prosecutor Marie-Therese de Givry denied that, saying police stayed on the scene until firefighters arrived.

Rioting and arson quickly erupted after the crash. The violence worsened Monday night as it spread from Villiers-le-Bel to other impoverished suburbs north of the French capital. Rioters burned a library, a nursery school and a car dealership and tried to set some buildings on fire by crashing burning cars into them.

Officials have pledged tough punishments for rioters: Eight people were convicted Tuesday in fast-track trials and sentenced to 3-10 months in prison, the regional government said.

Police reinforcements were moved into trouble spots north of Paris on Tuesday. Helicopters flew overhead, shining powerful spotlights into apartment buildings to keep people from leaving their homes.

Patrice Ribeiro of the Synergie police union said rioters this time included “genuine urban guerrillas,” saying the use of firearms – hunting shotguns so far – had added a dangerous dimension.

Police said 82 officers were injured Monday night, 10 of them by buckshot and pellets. Four were seriously wounded, the force said. Police unions said 30 officers were struck by buckshot.