Police have detained five Polish men in Wroclaw after fighting erupted in the wake of Poland's defeat to Czech Republic, which knocked the co-hosts out of the tournament.
The police were forced to use tear gas to separate the crowd and a spokesman said that the five most aggressive offenders were detained.
Speaking to Reuters, the spokesman Pawel Petrykowski said: "There was fighting between Polish fans. We moved in and had to use tear gas during the worst of the disturbance.
"The five most aggressive offenders have been detained."
Poland lost 1-0 to the Czech Republic, who went on to top Group A.