PARIS - French streets were relatively peaceful overnight after three weeks of unrest, police said Thursday. But protest has erupted amid suggestions that polygamy played a role in the violence.

Polygamy is illegal in France. But visas were granted freely to family members of immigrants until 1993, after which visas were authorized for only one spouse. The Ministry of Social Affairs estimates on its Web site that there are between 8,000 and 15,000 polygamous families in France.

France's League of Human Rights called the comments "sickening and irresponsible," while the anti-racist group MRAP said that such remarks would only feed the "racism and exclusion" that incited youths to riot.

Over the past three weeks, the rioting, spurred by widespread allegations of racism and discrimination, spread to nearly 300 towns and cities. Almost 3,000 youths - many French-born children of North and West African immigrants - have been arrested.

That debate over France's failure to integrate minorities grew more strident after Labor Minister Gerard Larcher was quoted in Wednesday's Financial Times as saying that youths from large polygamous families often had social behavioral problems, stemming from lack of a father figure...