Twelve police were wounded on Saturday in clashes with demonstrators in France's Savoie department where a protest against a high-speed rail project in the Alps turned violent, authorities said.
Some 2,000 protesters, including a roughly 300-strong dark-clad hardcore, were in the Maurienne Valley objecting to a tunnel for the link between Lyon and the Italian city of Turin.
They threw rocks at riot police, who responded with tear gas, and one demonstrator was wounded, local prefect Francois Ravier told a news conference.
"The day is not over, we remain prudent and mobilized," he said, noting a security presence would go through the night.
Interior Minister Gerald Darmanin tweeted the police injury toll. Border checks turned up 400 objects, like knives and hammers, while 96 individuals known by security services were sent back to Italy, the officials said.