Marauding youths set fire to cars, warehouses and a nursery school and pelted rescuers with rocks early Saturday, as the worst rioting in a decade spread from Paris to other French cities. The U.S. warned Americans against taking trains to the airport via strife-torn areas.A savage assault on a bus passenger highlighted the dangers of travel in Paris' impoverished outlying neighborhoods, where the violence has entered its second week. Attackers doused the woman, in her 50s and on crutches, with an inflammable liquid and set her afire as she tried to get off a bus in the suburb of Sevran Wednesday, judicial officials said. The bus had been forced to stop because of burning objects in its path. She was rescued by the driver and hospitalized with severe burns. Justice Minister Pascal Clement deplored the incident, saying it caused him "great emotion."