Manchester:Soccer fans fought with police on Tuesday outside Manchester United's stadium before and after the English team played AS Roma in the Champions League.
Before kickoff, fans from both clubs threw bottles and other objects at police lines outside Old Trafford and taunted each other with soccer chants.
There were reports of further clashes as Italian fans returned to the city center after United won 7-1 and advanced to the semifinals 8-3 on aggregate.
Twenty-one people were arrested, including seven Italians, Manchester police said.
Officers said that some of those detained were in possession of bladed and offensive weapons.
The violence, which started about three hours before kickoff, continued as the match started. Police described the incidents as "small and isolated."
"Due to the behaviour of a very small minority of United fans, police were forced to use batons and protective equipment, horses and dogs, in order to prevent the disturbance spreading," Superintendent Charlie Coxon said late Tuesday.
A group of about 1,000 mostly AS Roma supporters - some with "Invasion of Manchester" written in Italian on their shirts - gathered around the main entrance near a statue of former United manager Matt Busby.
Some were waving knives in the direction of the home fans.
"(Roma fans) charged down towards the stadium chucking bottles at United fans," United fan Rob Blanchette said. "Police beat them back into a corner."
No serious injury
The police had little success separating the fans and struggled to quell the standoff. Some fans had cuts and other injuries, but no one was initially believed to be seriously injured.
"The police started to run in our direction," Roma fan Riccardo Fartera said.
"There was about 10 minutes of a not-calm situation. I saw one boy about 20 years old being hit to the ground by the police and with blood pouring down his face," he added.
More trouble erupted later when a Roma fan threw a bottle at United fans while standing behind a police line. United fans then ran at the small group of Roma fans but were stopped by the police.
Alessandro Pinci said the visiting fans should have been given earlier access to the stadium.
"We just had to stand there and shield ourselves as the bottles came flying at us," Pinci said. "We were put in too much danger by being left outside the ground so late before the kickoff."
There was a heavy police presence for the match because of the trouble last week during the first leg in Rome, where Italian police clashed with United fans inside the stadium after Roma had scored its first goal.