PARIS — Dozens of far-right extremists have stormed the construction site of a mosque in western France to show their hostility toward it and denounce immigration that has brought millions of Muslims into the country.

Regional prefect Yves Dassonville said about 70 protesters traveled from around France for Saturday morning's demonstration in the city of Poitiers.

He said the protesters, convened by a group called "Coordination Identitaire," brandished banners, scaled the roof, and carried tents and electric generators for the protest starting shortly before dawn. Muslim leaders said they disrupted a prayer in the still-unfinished building.

Dassonville said that after police arrived, the protesters dispersed without resistance. Three were detained to face accusations of "incitement of racial hatred" and damage to property.

Interior Minister Manuel Valls denounced a "hateful and inadmissible provocation."