Violence broke out in the eastern town of Mulhouse over the weekend after rival gangs fought street battles, leaving at least six people injured including four police officers.
Local newspaper Les Denières Nouvelles d'Alsace reported that problems started after an argument between two families, of Chechen and north African origins, in the Bourtzwiller neighbourhood of the city.
On Friday, after a wedding at a mosque in the city, a group of young men started shouting insults at the marriage party.
Things got more serious on Saturday evening when fights broke out, this time with weapons, and police were called.
"We're not sure of the source of the tension," said Alain Martinez, director of public security for the region. "Around 40 people calling themselves Chechens turned up to settle an argument after a marriage that didn't end well on Friday." After the initial fighting, the Chechen men took refuge inside the mosque and found themselves circled by around 100 men from the neighbourhood. Police were required to help them evacuate. Police and the Chechen men were then subjected to a barrage of missiles including molotov cocktails, according to a police spokesman. A number of cars were also set on fire.
Police restored order later in the night and the area was tense but calm on Sunday evening.