"The UEFA Executive Committee has 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 ...including the potential disqualification of their respective teams from the tournament, should such violence occur again," UEFA said in a statement.
UEFA had earlier launched disciplinary proceedings against Russia in response to their fans storming their English counterparts in the stadium.
"We urge both the Football Association and the Russian Football Union to appeal to their supporters to behave in a responsible and respectful manner," UEFA said.