Bands of youths set fire to cars and trash bins overnight in a fourth consecutive night of vandalism mostly in immigrant neighborhoods of the Danish capital, police said. Seventeen people were arrested, Copenhagen Police spokesman Flemming Steen Munch said, adding police were not sure what sparked the violence. Some observers said immigrant youths were protesting against perceived police harassment and suggested the reprinting of a cartoon of the Prophet Muhammad in Danish newspapers Wednesday, may have aggravated the situation. "They feel provocations and discrimination by the police that stop then now and then to check them," Copenhagen social worker Khalid Al-Subeihi said. "It doesn't make it easier when the cartoons come back again."