'Chechen-Algerian gang war' erupts in French city
Police sources said the unrest - during which masked men were filmed wiedling axes and assault rifles - was sparked by an attack on a 16-year-old member of the Chechen community on 10 June.
Local reports said the Chechen teen had been attacked by older men from the Algerian community, although these claims have not been verified.
Following reports about the assault, members of the Chechen diaspora set out on so-called punishment raids, they said.
After three nights of violence, early Monday evening around 150 people, some hooded and armed, assembled in Dijon, setting rubbish bins and a car alight and shooting into the air.
"What happened is unprecedented and unacceptable," said the city's mayor, Francois Rebsamen.
Attacks had already taken place on three successive nights starting Friday, with many people wielding baseball bats.
The local prefect Bernard Schmeltz - the top state official in the region - said in a statement that the violence "appeared to be part of a settling of scores between members of the Chechen community in France and residents" of Dijon.
Police said that in one incident some 50 Chechens entered the restive district of Gresilles overnight Saturday, and a man who owns a pizzeria was badly wounded by apparent gunfire.
Even more people, around 200, also entered Gresilles late on Sunday with violent intent.
Footage circulating on social media showed large groups of masked men in body armour, waving guns, axes and other weapons.
In one video, a man insults the Chechens and tells the camera: "We are Arabs".
In an interview with local daily Le Bien Public, a man claiming to be a Chechen said the raids aimed to avenging an assault, by alleged local drug dealers, on the 16-year-old.
"There were about a hundred of us from all over France but also from Belgium and Germany. We never intended to ransack the city or take it out on the people," said the man, who was not identified by name.
Dijon prosecutor Eric Mathais said a total of six people had been injured in the three incidents on the successive nights, but no one has yet been arrested.
A probe has been opened into attempted murder by a criminal gang, he added.
Rebsamen said the police reinforcements were arriving after he spoke by telephone with Interior Minister Christophe Castaner.
Thirty-seven anti-riot police members came on Sunday, while 110 additional gendarmes will be deployed from Monday, he said.
Chechnya is a predominantly Muslim Russian republic in the North Caucasus. Two wars in the 1990s triggered a wave of emigration, with many Chechens heading for western Europe.
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