Wales supporters have been warned not to travel to France this week unless they have tickets for the England match.
Thursday's Group B game in Lens takes place 24 hours after Russia play Slovakia in the nearby city of Lille, and more English police are being sent to northern France in the wake of the weekend trouble in Marseille.
Several England fans have been jailed for their part in the disturbances, while a local prosecutor says "well-trained" Russian hooligans came to Marseille prepared for "hyper-violent" clashes.
Roy Hodgson and Wayne Rooney have issued an appeal to England fans ahead of this week's games, but there have been warnings of further violence from a prominent expert in hooliganism.
And the Football Association of Wales has urged ticketless fans to forget about making the trip to support their side.
"The FAW is advising fans not to travel to Lille and Lens for Thursday's match without a ticket," read a statement on the FAW's official Twitter account.