European soccer's governing body has warned the English and Russian soccer associations that their teams could be disqualified from Euro 2016 if there is a continuation of the fan violence that has injured several dozen people.
UEFA's threat came after it began disciplinary proceedings against the Russian federation on Sunday following ugly scenes inside Marseille's Stade Velodrome stadium at the end of Saturday's match between England and Russia.
Masked Russian fans charged at England supporters, punching and kicking them. Some England fans had to scramble over barriers to escape.
UEFA said that it would also investigate allegations of racist behaviour and the throwing of missiles and fireworks.
The violence in the stadium followed three days of clashes between English, Russian and French fans in the Mediterranean port city of Marseille, drawing a strong response from riot police.
UEFA said it was "disgusted" and would not hesitate to impose sanctions, including "the potential disqualification of their respective teams from the tournament, should such violence occur again".
"This kind of behaviour is totally unacceptable and has no place in football," UEFA said, adding that a decision on sanctions against Russia would be made on Tuesday.
Calling the behaviour of fans "barbaric", French Interior Minister Bernard Cazeneuve called for the two teams to be punished and said he had asked the cities hosting Euro 2016 fixtures to ban the sale and consumption of alcohol in zones where the risk of confrontation was most acute.
English and Russian fans will almost certainly cross paths in northern France later this week, with Russia playing Slovakia in Lille on Wednesday and England facing Wales only 40 km away in Lens on Thursday.
Russian Sports Minister Vitaly Mutko, who had initially denied that there had been any crowd disturbance, said that UEFA was right to investigate.
It is the second time in as many European Championship tournaments that the Russian federation has faced sanctions because of its fans.
Russia was fined and given a suspended six-point deduction for its Euro 2016 qualifying campaign after fans assaulted stadium security staff and displayed illicit banners at the 2012 tournament in Poland and Ukraine.
The British government urged calm on all sides and offered to send more police to France ahead of England's next game.
Violence also briefly erupted in Nice, where Northern Irish and local fans hurled glass bottles and chairs at each other late on Saturday.
Police said they had arrested 15 people after scuffles ahead of Sunday's game between Turkey and Croatia in Paris.
The French government rallied behind the police amid questions over tactics and security inside the stadiums.
"If there is a failure, it is that of soccer, which is sick because some of its fans drink excessively and fight," Interior Ministry spokesman Pierre-Henri Brandet said on BFM-TV.
A UEFA spokesman said that more security personnel would be deployed to segregate rival fans inside stadiums.