ROME — Activists poured mud and chocolate milk on the facade of St. Mark’s Basilica in Venice on Thursday in their latest climate protest, drawing a swift rebuke from the lagoon city’s mayor.

Police quickly detained the six activists. There was no immediate word of any permanent damage to the Byzantine basilica, an iconic symbol of Venice.

The activists from the Last Generation movement are demanding a 20 billion euro “reparation fund” to compensate Italians for climate-related damage. They cited the threat of rising sea levels on Venice as well as mudslides that have wreaked havoc recently on some Italian communities.

They said the liquid poured on the basilica’s facade and columns involved mud and Nesquik.

Venice Mayor Luigi Brugnaro condemned the protest as a “shameful and serious” act of vandalism. While acknowledging activists’ right to protest, he said they must “respect the law and our cultural and religious patrimony.”

The activists cited Pope Francis’s call to protect the environment. The Vatican tribunal recently convicted two Last Generation activists and ordered them to pay more than 28,000 euros in restitution after they glued their hands to the base of an ancient statue in the Vatican Museums to draw attention to their cause.

Other recent protests have involved activists blocking highway traffic in various parts of Italy, and gluing hands of activists to the protective glass of a Botticelli painting in the Uffizi Gallery.