Russians trained to fight were involved in the worst of the fan violence that erupted in Marseille at the start of the Euro 2016 soccer tournament, the French city's chief prosecutor said on Monday.
A middle-aged Englishman remained critically ill in hospital after he was assaulted, one of 35 people injured during three days of fighting involving Russian, English and French fans in Marseille's Vieux Port (Old Port).
European soccer's governing body, UEFA, has said it is "disgusted" by the melees inside and outside the stadium in Marseille and has threatened to expel the Russian and English teams from the championship if the violence persists.
Scenes of rival fans wielding metal bars and hurling beer bottles in street clashes in Marseille, as well as incidents in Nice, Lille and Paris, underscore the challenge soccer federations in Europe face in stamping out hooliganism.
Further along the Mediterranean coast from Marseille, Nice's prosecutor said violence there involving Northern Irish fans on Saturday night was instigated by remnants of the now-disbanded French fan group known as the Nice Brigade that had ties with far-right circles.
England fans have said they were ambushed by squads of Russian assailants in at least one incident, though the Marseille prosecutor made clear that England supporters were responsible for some of the skirmishes in Marseille.
Robin said trials would be held later on Monday for 10 people now in police custody - six Britons, three French nationals and an Austrian. All were charged with violence involving a weapon.
Asked why no Russians faced a court hearing, he said they had carried out lightning strikes which made arrests difficult and that closed-circuit television footage was still being studied. "These are highly trained people," Robin said.
Robin said some Russian supporters were turned back on arrival at Marseille international airport but that others had arrived overland.
French officials say 3,000 England soccer fans had been slapped with banning orders to block their travel to France due to previous offences, while only 30 Russian supporters were prevented from travelling.
A spokeswoman for British Prime Minister David Cameron said his government welcomed the UEFA investigation and it was also vital to review crowd-control methods inside Euro 2016 stadiums.
"Are there any lessons that the French authorities can learn from that for future games... to look at where the teams' relevant supporters are and how to manage those issues at the end of the game?" she told reporters.
Asked whether a complaint had been made about Russian fan behaviour, she said: "We have raised our concerns about the situation and want to look clearly at how we can improve it moving forward."