Twenty West Ham United fans have been arrested and another six injured during clashes with rival fans in Italy.
Up to 500 people were involved in the violence ahead of the Uefa Cup match against Palermo in Sicily on Thursday.
Rival fans threw bottles and chairs at each other when trouble flared at about midnight in the city's Teatro Massimo.
Riot police battled with supporters for more than an hour before putting West Ham fans on three buses which were driven away from the centre.
Virgilio Alberelli, of the Palermo police force, said officers were pelted with missiles as they tried to break up the brawl.
A total of 20 British fans and one Italian were arrested for violence against public officials while 109 other West Ham fans were stopped, identified and released.
Six officers, six English people and five locals suffered minor injuries.
Officials said more than 2,500 West Ham fans had travelled to the Sicilian capital for the second leg of the European competition, and security would be stepped up for the game.
Tension was already high after T-shirts bearing the slogan The Mafia were sold outside the east London club's ground ahead of the first leg earlier this month, which West Ham United lost 0-1.
A police spokesman said: "We had been alerted already ahead of the match and now we will be increasing security.
"Bottles, cans, glasses and chairs were thrown by both groups - it was a huge battle which took more than an hour to control.
"We would appeal for both sets of fans to keep calm and not react to provocation from opposition fans."
A spokeswoman from West Ham United said the club would not be releasing a statement about the violence.