Riot police moved into the western French city of Nantes on Saturday, clashing with hundreds of anarchists who broke shop windows, destroyed bus stops and pillaged the city centre.
At least eight police officers were hospitalized after violent confrontations with up to 1,000 "radicals," the prefecture of the Loire-Atlantique region said. Fourteen people were detained.
The rioters had joined an estimated 20,000 people protesting plans to build a regional airport. Officials did not say whether protesters were injured.
Interior Minister Manuel Valls said the delinquents were from the "radicalized ultra-left" and were waging an "urban guerrilla" campaign.
"These are individuals who are very violent." Valls said on iTele TV station.
'These are individuals who are very violent.' - Interior Minister Manuel Valls
Police used tear gas and water cannon to disperse the attackers, some wearing hoods and helmets. However, after night fall, approximately 200 were reportedly still roaming the Nantes city center.
There have been numerous, sometimes violent, demonstrations against the building of an airport in Notre Dame des Landes, a pet project of Socialist Prime Minister Jean-Marc Ayrault, a Nantes native. The anti-airport protests, mounted since 2009, have brought together an unlikely alliance of farmers, ecologists and anarchists — who call themselves ZADists, based on the French acronym for "development zone."
The farmers trying to save their land have depended on the ZADists to keep their protest alive.
It was unclear whether the ZADists were joined by even more radical elements. The interior minister referred to ultra-leftist groups also active in Germany, Italy and elsewhere.
The prime minister issued a firm condemnation of the violence, saying "nothing can justify it."