The mayor of Rome has accused Manchester United of creating a “negative climate” by warning supporters that they face “a real danger” of attack by hardcore Roma fans ahead of tonight’s Champions League quarter-final in the Italian capital.

Walter Veltroni is unhappy that United have told supporters who have travelled to Rome for the first leg to beware of the extreme “Ultras” element of Roma’s support.

The club's fans have also been warned in letters and in a statement on the club’s website against using the city’s underground network to reach the Olympic Stadium and to avoid certain areas of the city.

The statement, for “Roma-bound Reds” reads: “We realise that fans traveling independently may not wish to give up that independence but we ask you to consider your own safety and welfare as being of paramount importance.”

Mr Veltroni believes the advice is unnecessary and 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.

Rome’s chief of police, Achille Serra, also condemned the guidance. He told reporters: “Rome is one of the safest cities in the world. Obviously each team has small minorities of violent supporters, but to generalise or make this city out the way it has been in this letter is completely wrong and does not correspond to reality.”

United boss Sir Alex Ferguson claimed the letters were nothing out of the ordinary, adding: “Hopefully, everything will be okay. I don’t anticipate trouble but the Italian police are very experienced and I think they can deal with it.”

Last year, three Middlesborough fans were stabbed by masked “Ultra” Roma supporters, wielding knives fire-bombs and an axe, in a fight in a city centre bar. Today, sales of alcohol to fans have been banned from 3pm.

Around 5,000 United fans have bought tickets for tonight's game and a further 1,000 were expected to travel without tickets.