Youths rampaged for a third night in the troubled 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. Bands of young people set more cars on fire Tuesday in and around Villiers-le-Bel, the Paris suburb where the trouble first erupted, and 18 youths were taken into custody, the regional government said. In the south, 10 cars and a library went up in flames in Toulouse, police said. But France's prime minister said the situation was nonetheless calmer Tuesday than the previous two evenings. The government has attempted to keep violence from spreading, in what was shaping up to be a stern test for new President Nicolas Sarkozy. The unrest showed that anger still smolders in France's poor neighborhoods, where many Arabs, blacks and other minorities live largely isolated from the rest of society. Such neighborhoods burned in three weeks of rioting nationwide in 2005.