A football fan has been shot dead by police during a fight between rival supporters in Italy, officials say.
The victim was shot near a motorway restaurant in Tuscany
Local authorities said there had been a "tragic error" when police intervened to quell violence between fans of Roman team Lazio and Turin-based Juventus.
The victim, a Lazio fan, was on his way to a match at Inter Milan when he was shot at a rest stop near Arezzo.
Later hundreds of armed fans attacked a police barracks and the Italian Olympic Committee headquarters in Rome.
The Inter-Lazio game was postponed after the shooting and other matches started 10 minutes late, with players and officials wearing black armbands.
The Juventus fans were reportedly on their way from Naples to an away match against Parma.
"It was a tragic error," said Arezzo police chief Vincenzo Giacobbe.
"Our agent had intervened to prevent the brawl between these two groups, who had not been identified as fans," Mr Giacobbe said, according to the Italian news agency Ansa.
The victim was identified as Gabriele Sandri, a 26-year-old disc jockey from Rome.
He was apparently shot while in a car outside the motorway restaurant.
Gabriele Sandri worked as a disc jockey in the Italian capital
Police suggested the fan may have been killed by a warning shot.
The exact details of the shooting are unclear and an investigation is underway.
News of the death prompted anger among Italian fans.
In Bergamo, where Atalanta were playing AC Milan, police and fans clashed ahead of the match.
The game was abandoned 10 minutes after kick-off, when fans tried to smash down a barrier and force their way onto the pitch.
Sunday's late match between AS Roma and Cagliari in Rome was also postponed.
Rioters set vehicles alight near Rome's Stadio Olimpico
But a crowd of people wielding rocks and clubs turned up outside the Stadio Olimpico and attacked a police barracks and the HQ of the Italian Olympic Committee.
Security guards in the HQ barricaded themselves in as fans outside smashed windows and burned vehicles as they clashed with police.
The mob blocked off one end of a bridge over the Tiber and ordered motorists to leave the area.
Scores of police were injured.
In April the Italian government introduced a law aimed at stamping out football hooliganism.
It was enacted after a policeman was killed in rioting at a match in Sicily in February.