European soccer's governing body, UEFA, launched disciplinary proceedings against the Russian Football Union on Sunday after its fans assaulted English counterparts at the end of their Euro 2016 match in Marseille.
Moments after the final whistle in the Stade Velodrome, masked Russian supporters charged at England fans, punching and kicking them. Some England fans had to scramble over barriers to escape. UEFA said it was also investigating allegations of racist behaviour, the throwing of missiles and use of fireworks.
Russian Sports Minister Vitaly Mutko, who had initially denied that there had been any crowd disturbance, said UEFA was "right" to investigate.
The violence in the stadium followed three days of ugly skirmishes between English, Russian and French fans in Marseille, which drew a tough response from riot police.
In a statement, UEFA expressed its "utter disgust for the violent clashes that occurred in the city centre of Marseille, and its serious concern for the incidents at the end of the match inside Stade Velodrome.
"This kind of behaviour is totally unacceptable and has no place in football," UEFA said, adding that a decision on sanctions would be made within days.
Late on Saturday, fan violence spread to a second French city, Nice, where Northern Irish and local fans hurled glass bottles and chairs at each other.
France's government rallied behind the police amid questions over tactics and security inside the stadiums.
A UEFA spokesman said more security personnel would be deployed to segregate rival fans inside stadiums, particularly at high risk matches such as Sunday's Turkey-Croatia fixture in Paris.
He also said UEFA's executive committee was meeting to discuss how to react to the three days of violence in Marseille.
In the Mediterranean port city, some English fans suggested that French riot police had reacted heavy-handedly and been quick to fire tear gas. Thirty-five people were hurt in the fighting, including one English fan who suffered a heart attack.
Marseille police chief Laurent Nunez told France Info radio that his force's response prevented "much more serious damage". A total of 15 people were arrested in the city over three days.
While the tournament is being played under a state of emergency after Islamist militants attacked Paris in November, killing 130 people, French police will be under pressure to snuff out the fan violence.
"French police forces are not trained to deal with hooliganism," Driss Ait Youssef, a security expert, told BFM-TV. "You never know where a fight will erupt, so the challenge is to redeploy forces in a very short time span."
France has enlisted more than 90,000 police, soldiers and private security agents nationwide to ensure safety in the face of intelligence agency warnings of potential militant attacks and the threat of hooliganism.
"We can address both terror threats and fan violence," Marseille police chief Nunez said.