British police have urged England fans in Ukraine not to seek revenge for an attack that left three supporters needing hospital treatment in Kiev.
Some 30 hooded Ukrainians armed with knives are said to have set upon the fans in a coffee shop in a central area of the Ukraine capital.
Pictures of blood-splattered pavements quickly circulated on social media sites.
It is understood the three injured people have now left hospital and have opted not to co-operate with police investigations.
Around 2,000 England fans are expected to attend tomorrow night's game in Kiev's Olympic Stadium, and a win for England would move them to within touching distance of a place in next summer's finals in Brazil.
Police have reported a relaxed atmosphere in a city where there were no problems last year despite a much larger number of supporters for two games in Euro 2012.
Rachel Barber, head of the UK police delegation in the Ukraine, said: "We are aware of what happened last night and we will be going round most of the major bars, including this particular one, to make sure there are no problems.
"We would urge supporters to enjoy themselves but to do so without upsetting anybody. I am pleased to say that currently the atmosphere in the town is good, so in that sense what happened last night was out of the blue.
"Sometimes there can be an element of bravado on social media and you can never legislate for something happening but hopefully the England fans will just have a good time in what is a fantastic city."
A Foreign Office spokesman said: "We are aware of incidents in Kiev involving British nationals. We are providing consular assistance."