A protester was killed in unclear circumstances during clashes between police and protesters at the site of a controversial dam project in southwestern France.

Claude Derens, general prosecutor of the town of Albi, said it was "impossible" to determine the cause of death of the 21-year-old activist named Remi Fraisse.

Sivens dam protest
Forensic experts gather evidence at the site of the contested Sivens dam near the town of Gaillac where a 21-year-old man died in unclear circumstances during a violent clash between demonstrators and policeAFP
Sivens dam protest
Opponents of the Sivens dam project protest in Gaillac in memory of the 21-year-old man who was discovered dead on the site of the damAFP
Sivens dam protest
A protester lies on the ground surrounded by tear gas canisters and used flash grenadesAFP

Around 2,000 people had attended the protest against the Sivens dam project in woodlands located northeast of the city of Toulouse.

Ben Lefetey, a spokesman for the group Save the Testet Wetland, told AFP: "We are not saying that the security forces killed a protester, but a witness told us the death happened at the time of fighting."

Lieutenant Colonel Sylvain Renier of the Tarn police said between 100 and 150 "anarchists" wearing hoods threw incendiary devices at the security forces at around 2am, and the police used tear gas, stun grenades and flash balls in return.

Sivens dam protest
Riot police arrest a protester amid clouds of tear gas in GaillacAFP
Sivens dam protest
Police confront opponents of the Sivens dam project during a protest in Gaillac in memory of Remi FraisseAFP
Sivens dam protest
A fire burns as riot police clash with opponents of the Sivens dam project in GaillacReuters
Sivens dam protest
A sign reading "homage to Remi" is seen on a barricade built at the site of the contested Sivens dam near the town of GaillacAFP

Local residents and environmental activists have been protesting against the deforestation of the area for a couple of months, employing tactics such as burying themselves up to their necks in the road, and staging hunger strikes.

The Tarn council states that the dam would supply much-needed irrigation to surrounding farms, but activists argue it would kill off wildlife, including 94 protected species that reside in the forest.

Sivens dam protest
Demonstrators, some of them half-buried, block one of the entrances of the construction site of the Sivens dam on 8 September, 2014AFP
Sivens dam protest
An environmental activist confronts a riot policeman securing a construction site in the Sivens forest, on 9 September, 2014AFP
Sivens dam protest
Riot police apprehend an environmental activist during skirmishes on a construction site in the Sivens forest, on 9 September, 2014AFP