Police chiefs, politicians and football administrators are meeting in Italy to discuss violence that erupted after a policeman shot dead a fan in Tuscany on Sunday.
Police said the killing, in the city of Arezzo during clashes between rival fans, was "a tragic error". It triggered violence in Rome, Bergamo and Milan and resulted in several Serie A matches being cancelled.
In February Italy's football programme was badly disrupted after a police officer was killed in a riot in Catania following a Sicilian derby match.
New measures were introduced and stadium security was tightened in an effort to dampen hooliganism but authorities may have to look again at the laws amid calls to ban away fans from all grounds in future.
Prime Minister Romano Prodi has called for a full investigation into Sunday's shooting, and described the violence as "very worrying".
The fighting broke out after Gabriele Sandri, 26, was hit in the neck by gunfire at a motorway service station. He was he hit while sitting in a car as police tried to stop fighting between Lazio and Juventus supporters.
Mr Sandri, a disc jockey from Rome, was a Lazio fan on his way to a match with Inter in Milan. The match was postponed just hours before kick-off after emergency talks between the Lega Calcio and the club officials.
The unnamed officer under investigation for firing the fatal shot could not believe he had hit the victim. "I didn't point it at anything, I didn't aim at anybody," he told Corriere della Sera newspaper.
"The first shot I fired into the air and the second left me while I was running. Now I have destroyed two families, the man's and mine."
As news of Mr Sandri's death emerged, angry fans took to the streets in several parts of Italy. The worst of the violence came in the evening in Rome - home of Lazio - where hundreds of armed fans blocked off one end of a bridge over the River Tiber.
Sunday's late match between Roma and Cagliari in the capital was also postponed but supporters wielding rocks and clubs turned up anyway outside the Stadio Olimpico.
The mob attacked a police barracks and the city headquarters of the Italian Olympic Committee (CONI), the body which oversees all sport in Italy.
Security guards in the CONI headquarters barricaded themselves in as fans outside smashed windows and burned vehicles during clashes with police. A bus was torched and several people were injured, including police.
"It is another very sad and painful day for all of Italian football," Italian Football Federation (FIGC) President Giancarlo Abete said in a statement.
"The first thought is of huge condolences for the family of Gabriele Sandri."
Abete said in the statement he had convened a meeting for later on Monday with his board as well as representatives of the Lega Calcio, and player and manager's associations.
They will discuss what to do about the Inter-Lazio and Roma-Cagliari matches, which were postponed because of the shooting and whether to play the Atalanta game or award the points to Milan.
Across Italy seven of the Serie A matches started 10 minutes late. Players wore black armbands but atmospheres remained tense.
In other developments:
- Fans in Milan hurled rocks at a police station and beat up two journalists.
- Supporters in Siena shouted "murderers" at police.
- There was also violence at lower league in Serie C in southern Italy.
- As an investigation into the shooting of Mr Sandri was launched, police suggested he may have been killed by a warning shot.
Arezzo police chief Vincenzo Giacobbe told Italian media: "It was a tragic error.
"Our agent had intervened to prevent the brawl between these two groups, who had not been identified as fans."
A report last month said injuries at stadiums caused by fan violence had dropped 80 percent from last season but Abete has often said that football authorities can do little to stamp out trouble away from stadiums.
The clash between Lazio and Juventus fans that led to the accidental shooting happened at a motorway service station in the Tuscan city of Arezzo, far from any stadium.
The matter is complicated because Juve fans in particular live across Italy, not just in their base of Turin, meaning fans travel huge distances to see their team and often come across rival fans on routes not usually associated with football traffic.
Abete has also been at pains to point out that the shooting was very different from February's death and that the response should be measured.
"The loss of a life is always unacceptable but objectively the dynamics of the dramatic episode is totally different from the killing last February of inspector Filippo Raciti at Catania," he said.
There is a break in the Serie A programme next week because Italy visit Scotland in a crunch Euro 2008 qualifier on Saturday, and host the Faroe Islands four days later in Modena, giving authorities some time to decide on the next step.
If Italy lose the world champions will be in danger of not reaching next year's finals in Austria and Switzerland, which could cause more tension among fans.