Months of tension between police and young people in a troubled district of northern France exploded on Tuesday, with dozens of youths facing off against riot officers in a night of violence. Sixteen officers were injured, a pre-school and public gym were torched, and at least three passing drivers in Amiens were dragged from their cars.

While the identity of the rioters and the immediate cause is unclear, the economic picture of the area in question is not. Unemployment skews higher in northern France and among the country's youth. Less than two weeks ago, the French government declared Amiens among 15 impoverished zones to receive more money and security.

The eruption of violence shows how little relations have changed between police and youths in France's housing projects since nationwide riots in 2005 raged unchecked for nearly a month, leaving entire neighborhoods in flames in the far-flung suburbs.

At the height of the latest confrontation, 150 officers _ both local and federal riot police _ faced off against the young men who fired buckshot and fireworks at them, skirmishing through the neighborhood in the city about 75 miles (120 kilometers) north of Paris. There were no arrests.

"The confrontations were very, very violent," Amiens Mayor Gilles Dumailly told the French television network BFM. Dumailly said tensions had been building for months between police and the impoverished residents, whom he described as "people who are in some difficulty."

Relations between police and youth in housing projects have been troubled for years, perhaps decades. Riots occasionally erupt, often in the hot nights of August, when France's rich and middle classes head off for long vacations but poor and immigrant families in the projects stay home.

Alain Bauer, a professor of criminology, said circumstances had only worsened since 2005. He said it was hard to predict what would happen after the Amiens violence, which he described as "a culmination of bitterness and tension."

"These are small events that stand apart unless they take on greater importance," he said. "It will take an in-depth reaction (from the government), responding to both criminal and social problems."

The riots usually follow a pattern: Police target a kid speeding on a motorbike or doing something suspicious; the kid speeds or runs away to escape and dies or gets seriously injured in flight. The neighborhood rises up in anger and that night or the next, young people head out to burn cars, police stations or any building representing authority. Police often respond by coming in force with tear gas, further angering the local population.

The same Amiens neighborhood saw violence last summer, when police and firefighters responding to a car fire came under attack by about 20 young men throwing stones.

Police in Amiens said the latest riot involved about a hundred young men and began around 9 p.m. Monday, ending around 4 a.m. after federal reinforcements arrived. There had been smaller confrontations with police over the past week, including one involving a weekend traffic stop that some local residents thought was unnecessarily heavy-handed.

Until Monday night, the violence in Amiens had been on a smaller scale. By the time the latest confrontation was over, two school buildings had been burned, along with a dozen cars and trash cans used as flaming barricades. At least three bystanders were hurt when rioters yanked them from their cars, police said.

Earlier this month, the district in Amiens was among 15 areas declared the most troubled in France, and the government pledged more security and more money. Dumailly said he had hoped tensions would improve with a plan to fix up the housing projects and offer more services.

"Public security is not just a priority but an obligation," French President Francois Hollande said Tuesday, speaking at a memorial for two gendarmes killed in June. "We owe it to the population, we owe it to the security forces."

He mentioned the violence in Amiens, as well as unrest in Toulouse, in southern France, where rival groups in two housing projects have been battling for a number of days. The violence marked the first major unrest under Hollande, who took office in May.

Unemployment stands at 12 percent in northern France, compared with 10 percent nationwide. Among French ages 15-24, unemployment stands at 23.3 percent, according to the national statistics agency.

French Interior Minister Manuel Valls was expected in Amiens on Tuesday afternoon.