Marseille hit out at a "frenzy of violence" as their game against Rennes in France's Ligue 1 on Saturday was postponed after hundreds of angry supporters broke into the club's training ground and caused widespread damage in a protest.
The hardcore Ultras, who were demonstrating against the club leadership and the team's poor recent run of results, assembled in the afternoon in front of Marseille's La Commanderie training ground, throwing smoke bombs and firecrackers.
"Several hundred Ultras used force and violence to get into the training ground, including the first team's building," the club said in a statement.
"A frenzy of unjustifiable violence put the lives of those present in danger. Thefts were committed and vehicles damaged. Five trees were burnt down...several hundred thousand euros worth of damage was caused."
Local police in France's Bouches-du-Rhone department earlier said 25 arrests were made and seven police officers were injured after "300 OM supporters violently attacked police officers present to secure La Commanderie".
Sports daily L'Equipe reported that Marseille's Spanish defender Alvaro Gonzalez was struck on the back by a projectile as he went to confront the supporters.
"We are all astonished: staff, coaching staff and players. We were not expecting a savage horde to turn up and destroy everything," Marseille president Jacques-Henri Eyraud told Canal Plus.
"I think we avoided an even worse situation. It could have been a tragedy. Everyone is shocked, players and staff. These are not real supporters, they are hooligans, delinquents, people who have no respect for anything."
The French league reacted to the incidents by postponing Marseille's home game against Rennes, scheduled for Saturday evening, "to a later date", even though it was due to go ahead behind closed doors due to the Covid-19 pandemic.
Marseille were second in Ligue 1 when last season ended early because of the pandemic. However, they have lost their last three league matches and have slid 14 points behind leaders Lyon, albeit with two games in hand.
A 2-1 win for Lens at Montpellier on Saturday saw Marseille slip to seventh place.
They have won just one of their last nine games in all competitions and are due to visit Lens in midweek before hosting fierce enemies Paris Saint-Germain next weekend.
On Friday coach Andre Villas-Boas admitted he expected to leave at the end of the season.
"The place needs a clear-out... I'm responsible for the results and right now they're awful," the Portuguese former Porto, Chelsea and Tottenham Hotspur coach said.
For several weeks supporters have organised protests before home matches, which are all being played behind closed doors.
On Saturday an increased number of banners attacking club leadership, including Eyraud, were hung around the city on motorway bridges, roundabouts and even the Corniche overlooking the Mediterranean Sea.
"Follow AVB, get out of here", "Parisians, get out of here", "Give us back OM", read some of them.
Eyraud, who was born in Paris, was a frequent target after he angered fans during a conference on management when he talked about the "danger" of having too many Marseille residents or club supporters working at the club.
"JHE: No Marseille fans at OM? Get out of here", said one banner unfurled above a motorway, and "JHE, Marseille vomits you out" said another at the Prado roundabout, a few metres from the Stade Velodrome.