There have been clashes in several French cities after a man protesting against a controversial dam project was killed in a confrontation with police.
A prosecutor said that Remi Fraisse, 21, died of wounds caused by "an explosion".
His body was discovered in the early hours of Sunday morning after rioting in Albi in southern France.
There was violence in Albi, Nantes and Rennes as hundreds of people protested against Mr Fraisse's death.
Protests were also held in Paris, Brest, Lyon and Marseille.
In Nantes, more than 600 demonstrators walked through the streets carrying banners calling for solidarity against police violence, French media reported. Windows were broken and police used tear gas to halt the unrest.
Since 2012, Nantes has seen several violent protests from environmentalists over the construction of a new international airport.
There were outbreaks of violence in Albi as well, where some 1,000 people rallied in the city centre chanting "Remi, Remi we won't forget you".
Mr Fraisse died following a demonstration against the Sivens dam project in the south-west region of Tarn late on Saturday.
Opponents of the dam scheme say it will harm the environment, but officials say it is necessary to boost the local economy.
A crowd of 2,000 people had gathered peacefully but fighting broke out later, in which he was fatally wounded in back and seven police were also hurt.
His body was found in the early hours of Sunday as protesters continued to throw petrol bombs and police responded with tear gas and stun grenades.
On Monday a prosecutor said that it was not clear who exactly was responsible for the "explosion" that caused Mr Fraisse's injuries.
He was referring to media reports that it was triggered by a grenade thrown by police.