Violence erupted when about 20,000 people demonstrated against an airport project near the city of Nantes on Saturday, leaving six riot police officers injured.
The protest on Saturday in Nantes, homeland of French Prime Minister Jean-Marc Ayrault, involved around 20,000, according to police, and was the first since local authorities gave the project a green light.
The protesters, including farmers, locals and green politicians, argue the new airport will damage the environment and is a waste of public money during an economic crisis.
Police have tried several times in vain to evict the squatters and have had to contain many demonstrations.
Riot police used tear gas to disperse protesters who lobbed projectiles and threw paint onto Nantes' city hall, set fire to construction vehicles and vandalized the offices of Vinci, the project's contractor.
"In democracy the right to contest and manifest against a project is legitimate, but this violence is unacceptable and nothing can justify it," French Interior Minister Manuel Valls said. "I regret that this demonstration transformed itself into a genuine urban guerrilla, escaping the organizers' control," he added.
The 580-million-euro airport, named Notre-Dame-des-Landes, is planned to be finished in 2017.
