POITIERS - Dozens of political extremists late on Saturday 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 some 70 protesters, travelled from around France for Saturday morning’s demonstration in the city of Poitiers, climbed atop an unfinished mosque in western France to show their opposition to it and the spread of Sharia law.

He said the protesters, convened by a group called Generation Identitaire, brandished banners, scaled the roof, and carried tents and electric generators for the protest starting shortly before dawn.

The mosque is in the city of Poitiers, where Charles Martell drove away Muslim invaders in 732. The protesters hung a banner on the mosque that read “Generation Identitaire” and demanded a referendum on immigration and mosque construction. The banner also included the number 732. After police arrived, the protesters left peacefully and three were detained for “incitement of racial hatred” and damage to property.

Muslim leaders, who aren’t used to this kind of thing in France, expressed incomprehension over the stunt. “We are thunderstruck ... these are people who are stuck in the year 732, and who don’t see that the world has changed,” Poitiers imam El Haj Boubaker told France’s BFM-TV. “People can live differently than in a mindset of war and conflict.”

Interior Minister Manuel Valls denounced a “hateful and inadmissible provocation” by the protesters.