England and Russia have been threatened with expulsion from the European Championship if there is further violence by their fans.

Expressing its "utter disgust" over three days of disorder in Marseille, UEFA told the English and Russian federations on Sunday "to appeal to their supporters to behave in a responsible and respectful manner" at the tournament in France.

Only Russia is facing immediate UEFA disciplinary proceedings after its fans attacked English rivals inside the Stade Velodrome after their first match in Group B, which ended 1-1. But English fans were at the heart of days of mayhem in Marseille's Old Port district, which also involved French and Russian fans.

The governing body said its executive committee "warned both football associations that — irrespective of any decisions taken by the independent disciplinary bodies relating to incidents inside the stadium — it will not hesitate to impose additional sanctions on the Football Association and the Russian Football Union, including the potential disqualification of their respective teams from the tournament, should such violence occur again."

The English FA responded by saying it treats the UEFA warning with the "utmost seriousness."

"We understand the potential implications of our supporters' actions and wholly accept that every effort needs to be made by the FA to positively urge them to act in a responsible and respectful way," the FA said.

UEFA's robust warning to England and Russia followed emergency meetings to discuss the clashes as well as the security measures inside the 10 stadiums being used across France for the 24-team tournament.

"UEFA acknowledges that there were segregation issues at Stade Velodrome and will implement corrective measures to strengthen the deployment of security personnel at stadiums, in close collaboration with local authorities," UEFA said.

Russia has been charged by UEFA over crowd disturbances, racist behavior by fans and the setting off of fireworks at the game. UEFA's disciplinary body will judge the case on Tuesday, imposing sanctions ahead of its second Euro 2016 game against Slovakia on Wednesday in Lille.

When UEFA's disciplinary panel judges incidents in Marseille, it could take Russian fans' track record at Euro 2012 into account. UEFA imposed a series of sanctions, including fines, on the Russian Football Union for incidents at that tournament, which was hosted by Poland and Ukraine.

Although UEFA holds national federations responsible for their fans' behavior inside stadiums, it typically does not act on incidents elsewhere.

England's next game is a British derby against Wales in the Lens on Thursday, a day after Russia plays Slovakia in nearby Lille.

"We are not worried about the game going ahead on Thursday," FA chief executive Martin Glenn said. "Our worry there is lower."