Escalating soccer violence in Brazil has sparked fears of a new wave of confrontations in South America's biggest city.
A 21-year-old Palmeiras supporter was fatally shot in the head in Sao Paulo in a fight involving nearly 500 fans Sunday.
This was the second soccer-related death in just more than a week in the country that will host the 2014 World Cup. There hadn't been a death linked to fan fighting in Brazil since early last year, when a Corinthians fan was killed in Sao Paulo.
There have been clashes between rival fan groups nearly every week this year, and authorities said on Monday they will meet in the coming days to try to establish the causes of the renewed violence.
The Sao Paulo state football federation said it is banning the two fan groups involved in Sunday's fight from entering stadiums.
"The strategy that was in place before is not working anymore and something needs to be done to make sure these cases don't happen anymore," Sao Paulo state prosecutor Thales Cezar de Oliveira told The Associated Press.
Oliveira acknowledged there is a sense of urgency because Sunday's death could generate more violence.
"Without a doubt police will have to stay on alert now," Oliveira said. "They will have to monitor this situation closely to keep another incident like this from happening."
Andre Alves was killed when hundreds of Palmeiras and Corinthians fans confronted each other Sunday morning in Sao Paulo's north side, using iron bars, pieces of wood and rocks as weapons. Another Palmeiras fan was shot in the hip, and two others remained hospitalized with head injuries, one of them in serious condition, according to local authorities.
Riot police were deployed and had to use tear gas and rubber bullets to halt the confrontation. They detained four people, including two suspected shooters.
The fight happened several hours before the teams met in the Sao Paulo state championship, more than 6 miles from the Pacaembu stadium where the match occurred. Authorities were investigating reports the fight was set up through social media networks.
"This match is seen as a championship in itself, but it has to be a healthy rivalry," Corinthians coach Tite said. "There has to be a limit."
Authorities believed Sunday's confrontation might have come in retaliation for the death of a Corinthians supporter early last year in an ambush by a Palmeiras fan group, a fight that didn't happen on a match day.
"We need to do something to stop this right now," Oliveira said. "If they keep starting these fights to avenge a death, they will never end."
A few days ago, a 28-year-old fan of small club Guarani died of head injuries after fighting with Ponte Preta supporters in the interior city of Campinas, about 60 miles from Sao Paulo. The death prompted authorities to ban the teams' fan groups from stadiums.
Fan groups from the top Sao Paulo state clubs, Palmeiras, Corinthians, Sao Paulo and Santos, have been involved in several incidents before matches this year, but there have been problems in other parts of the country too.
Four Goias fans were wounded by gunshots in Goiania in January, and another four were shot after a fight that left 80 people detained in Rio de Janeiro late last year.
In November 2010, a 19-year-old Cruzeiro fan was killed after being repeatedly beaten with iron bars during a brawl between dozens of rival fans in Belo Horizonte in southeastern Brazil.
Oliveira said several actions were in place in Sao Paulo to help combat fan violence in the last few years, including a close relationship with the fan groups, the prohibition of alcoholic beverages inside the stadiums and the decrease in the number of fans at away matches. Banning fan groups from stadiums may be an option now, although similar measures in the past did not prompt satisfactory result.
Experts said Monday that the lack of severe punishment and proper police training are some of the reasons for the continued violence. They say authorities need to take a more active role.
"They are being too passive in relation to this problem and this is what ends up happening," said Mauricio Murad, a sports sociologist with the UNIVERSO university in Rio de Janeiro. "We need better trained police and proper punishment to try to contain this problem."
Murad conducted a study a few years ago that showed that more than 40 people were killed in connection with Brazilian soccer matches between 1999 and 2009.
He said the problem is mostly isolated to fan groups and this kind of fan violence should not cause concerns for events such as next year's Confederations Cup and the 2014 World Cup.
"It's a different issue," he said.
Other South American nations have had to deal with fan violence recently. One man was killed and dozens were injured in two separate instances in Colombia this month.