A group of English football fans have been injured in a late-night clash in Rome ahead of a Europa League match.At least nine Britons and one American were hurt when masked assailants attacked a pub in the Italian capital, according to police.The Britons were in the country to support Tottenham Hotspur who are due to play Lazio at the Stadio Olimpico on Thursday night.They were set upon by knife-wielding "Ultras" - fanatical fans - when they were enjoying a drink at The Drunken Ship pub, according to reports.Blood stained the cobblestones outside the bar, chairs and bits of wood were strewn across the floor, and windows were broken.Briton Ashley Mills was stabbed and was in serious condition, police said, and the American was also stabbed."We understand from local police that nine of our supporters suffered injuries last night following an incident in the city centre. Three of these supporters were taken to hospital for further treatment," said a statement from a Spurs spokesman.Police said around 50 Italians were involved in the assault, and that some had been arrested.The aggressors, who were believed to be Lazio fans, had their faces covered by motorcycle helmets or scarves when they launched their assault shortly after 1am.Italian newspaper La Repubblica described the clashes as "urban warfare" and reported that up to 100 "Ultras" armed with knives, baseball bats and belts had taken part in the attack.Witness Giuseppe Tamborra said: “I saw four people lying on the ground, one with his forehead cut open from here to here, probably with a stool taken from the bar."The Italians were very organised, with helmet, bats, even balaclavas," he said.The Drunken Ship, a popular drinking spot for tourists and foreign students, is located in the Campo de Fiori -- one of the most visited squares in the Italian capital's historic centre.The square features a colourful food market and a vibrant nightlife, and the American-owned bar is renowned for its lively atmosphere.There was no response from the pub on Thursday morning.A Foreign Office spokesman confirmed they are investigating the clash.