A 21-year-old activist died Saturday night after a violent clash between police and demonstrators at the site of a controversial dam project in the Sivens Forest in southwest France. More than 2,000 environmental activists gathered in the woodlands for a rally that turned violent when militants attacked security forces.

Speaking to radio station France Info, local prosecutor Claude Derens said that the initial results of a post-mortem examination confirmed that the man died as a result of an explosion. Derens also stated that it was too early to know yet if the death was caused by a grenade blast, a hypothesis put forward by several witness statements. Investigations are still underway, and further results are expected tomorrow.

The timing of the autopsy coincides with the publication of a report commissioned by the French Ministry of Ecology that criticizes the decision by local officials to proceed with the construction of the controversial dam. Eco-activists argue that the dam, which would provide irrigation to surrounding farms, poses a huge environmental threat to the biodiverse Sivens wetland.

According to VICE News sources, between 2,000 and 5,000 people gathered on Saturday in Sivens, a forest about 400 miles south of Paris. What began as a friendly and cheerful rally was disturbed by the arrival of two high-profile French politicians, Jean-Luc Mélenchon and José Bové, accused by some activists of highjacking the environmental agenda.

According to website Reporterre, in the middle of the afternoon protesters followed a shepherd leading a flock of sheep from the Métairie — a farm building that has served as a headquarters for the activists — across the site of the future dam, which is now an open space where the forest has been cleared.

VICE News spoke to one of the demonstrators, Émilien (who declined to provide his real name), about the events that unfolded Saturday afternoon. According to Émilien, the march with the sheep started after 3pm and included "a large number of demonstrators."

"We walked across the deforested area and arrived at the other end of the site, where there is a fenced-in area, usually reserved for the workers," he said. "There were no machines on site, only seven or eight busloads of riot police."

Émilien said there was no altercation with the police, and the procession remained in the clearing peacefully. The police were apparently stationed there to stop demonstrators from entering the enclosure, which, according to Émilien, contained only a charred container and trailer. The flock of sheep and the bulk of the demonstrators then returned to the Métairie, at the other end of the clearing. Émilien said roughly 100 masked protestors, dressed in black, arrived from the Métairie equipped with various objects used as shields.

"They stopped all together around 350 feet from the police," he said. "They marched toward the riot police, hurling stones and Molotov cocktails. The riot police's reaction was quick. Within minutes, several police trucks arrived with backup, 14 trucks in total. The clash reached a climax: lots of tear gas and stun grenades — at least one every five minutes. Because of the [Molotov] cocktails, some fires broke out on a hilly area overlooking the fenced-in area. Firefighters responded in clouds of tear gas. I could still hear noise from the clashes when I left the Testet area at around 8pm."

On Sunday morning, the Tarn prefecture in Albi released a statement: "Tonight, at around 2am, gendarmes discovered the body of a man on the Sivens site. Firefighters intervened rapidly only to find out that the victim had already passed." At this point, the victim's identity and the circumstances surrounding his death had still not been established.

VICE News met up with Camille (not her real name), an eco-activist who was also present Saturday at the Métairie, which is also known as the ZAD (Zone to Defend). According to Camille, a medical team assisted 15 wounded protesters with injuries to the arms and legs from stun grenades. Camille said that she had seen this type of injury at other protests, such as the demonstrations against an airport at Notre-Dame-des-Landes in early 2014. She also reported two head injuries caused by the tear gas canisters, and others she claims were caused by flash-balls.

"Things calmed down around 5pm," she said. "In the night, there were several big clashes, between 8pm and 4am. It wasn't continuous fighting. The police used their whole arsenal of weapons: flash-balls, stun grenades, tear gas… the whole lot. Apparently, that's when a guy died around 2am."

According to Camille, the police had left the ZAD by Sunday morning when the demonstrators returned to the site of the clashes.

"We found a trail of blood, it looked like someone had been dragged across the ground over several meters," she said. "We took pictures. But we don't know if this has anything to do with the person who died."

On Monday morning, Reporterre published photographs of the trail of blood, along with several witness statements, one of which claims the young man was hit by a grenade or a flash-ball.

In an interview with AFP on Sunday, Ben Lefetey, a spokesperson for the group Save the Testet Wetland, said that "the death occurred during clashes with the gendarmes at around 2am." He said that a witness saw a person fall to the ground during the clashes and be taken away by the police. "We are not saying that the police forces killed a protester, but a witness told us the death happened at the time of the clashes," Lafetey said.

Mid-afternoon on Sunday, prosecutor Claude Derens held a press conference about the clashes. He said that police spotted the man while scanning the area with flashlights, and confirmed that the man, who was identified by his phone, is called Rémi and is 21 years old. Speaking this morning on i-Télé, the man's father claimed that his son "was not one of the radicals".