Manchester United have been accused of raising tensions by warning fans they could be attacked ahead of the Champions League clash against Roma.
United fans have been warned not to travel by metro to the stadium
The city's mayor Walter Veltroni is unhappy the club have told travelling supporters to beware of the hardcore "ultras" element of Roma's support.
Fans have also been warned in letters and on the club's website to avoid certain areas of the city.
Mr Veltroni believes the advice could create a "negative climate".
He told Italian sports daily Gazzetta dello Sport: "Rome is a city that welcomes everyone in a hospitable manner.
"I consider what appeared on the Manchester United website to be an unfortunate accident, but also dangerous because it risks creating a negative climate.
"I have spoken on the telephone to the English ambassador. Rome is a serene and welcoming city."
About 5,000 United fans have bought tickets for the first leg of the quarter-final tie and a further 1,000 could travel without tickets.
Supporters began arriving in Rome on Wednesday morning having been warned to avoid using the city's underground network to reach the Olympic Stadium, and to also keep away from the Ponte-nenni bridge and the Campo de Fiori.
United boss Sir Alex Ferguson claimed the letters were sent ahead of every European tie and were not out of the ordinary.
"We always issue a letter for every away trip," he said.
"More importantly, the Italian police have been very communicative with our people.
"Hopefully, everything will be ok. I don't anticipate trouble but the Italian police are very experienced and I think they can deal with it."
Three Middlesbrough fans were stabbed and 10 others hurt during fights with Roma fans when the teams met in the Uefa Cup quarter finals in 2006.