COPENHAGEN, Denmark (AP)  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." The youths set dozens of fires in several districts of Copenhagen, torching cars and trash bins and in some cases hurling rocks at police. Newspaper Jyllands-Posten said one of its photographers received minor injuries when he was attacked by vandals in the Noerrebro district. It was not immediately clear whether the attackers knew he was working for Jyllands-Posten, which first printed the 12 cartoons of the Prophet Muhammad that sparked massive protests in Muslim countries two years ago. More than a dozen Danish newspapers reprinted one of the cartoons on Wednesday in a gesture of solidarity after police revealed an alleged plot to kill the creator of the caricature. Munch said he did not know whether the reprinting of the cartoon had any part in the violence. "We see different reasons for the rioting," Munch said. "We do not know why exactly. It can be because of boredom, it can be because police in recent weeks have stepped up its search for knives, it can be other things too." There were also reports of vandalism in Aarhus, Denmark's second-largest town, but no arrests were made. Copyright 2008 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed. Conversation guidelines: USA TODAY welcomes your thoughts, stories and information related to this article. Please stay on topic and be respectful of others. Keep the conversation appropriate for interested readers across the map.