There are "serious concerns" about security in Lille, where England and Russia fans are set to gather for this week's Euro 2016 matches, Football Association chairman Greg Dyke says.
England fans are due to be in Lille ahead of Thursday's match against Wales in nearby Lens, while Russia play Slovakia in the city on Wednesday. Six England fans were jailed after the teams drew 1-1 on Saturday. Russia has received a suspended disqualification from the tournament. The country was also fined 150,000 euros (£119,000) over crowd trouble at the match in Marseille.
Uefa said the punishment would be imposed if similar incidents happen at any of Russia's remaining matches.
Meanwhile, Home Secretary Theresa May described the violence as "deeply disturbing" and said the UK was offering support with investigations and "post-incident analysis". Both Russia and England could face expulsion by Uefa, the organisers of Euro 2016, if there is any further violence.
But in a letter to Uefa in response, Mr Dyke rejected the suggestion that England fans were at fault for scenes inside the Stade Velodrome following the match with Russia. He said that the implication that English fans were in part responsible was "contradicted both by the video evidence and by the fact your independent disciplinary bodies have only instigated sanctions against the Russian Football Union". England fans, particularly those without match tickets, had been advised to stay in Lille because Lens is a small city, Mr Dyke said. "We have serious concerns around the security arrangements for the city in the next few days," he added. "These concerns are heightened with the knowledge that Russia will play in Lille on Wednesday afternoon."
Thousands of supporters are expected to follow Thursday's match between Wales and England at fan zones in the Place Jean Jaures in Lens and also Lille, which is 24 miles (39km) away. More than 35,000 ticket holders are due to watch the clash in the Stade Bollaert-Delelis. Responding to an urgent Commons question from shadow home secretary Andy Burnham, Mrs May said the UK was sending police spotters - officers trained to spot trouble-makers at football matches - to support French authorities. This will involve the deployment of additional British Transport Police officers on rail services in the area, following a request from the French. She also said 1,400 passports were seized from England fans before the tournament began. England fans without tickets were being advised against travelling to Lens and Lille, she added.
