SAO PAULO (AFP) - Protesters went on a rampage in Brazil's largest city, smashing windows and teller machines and battling riot police in a fresh bout of violence blamed on the "Black Bloc" anarchist group.
Police fired tear gas and arrested 92 people during the disturbances late Friday, which began as a peaceful march to demand free public transportation for students before turning violent.
Sao Paulo's military police said a police colonel was mobbed and beaten by a group of "criminals disguised as protesters" who stole his pistol and radio.
President Dilma Rousseff expressed her support for the injured police officer, Reynaldo Simoes Rossi, and denounced the violence as "anti-democratic barbarities." "The security forces have an obligation to ensure that demonstrations take place in a free and peaceful manner," she said.
Images released by police showed masked assailants swarming the colonel as another police officer, pistol in hand, tried to defend him.
"The officer has a broken collarbone and multiple abrasions on his face and head," a police statement said.
It said those arrested were being held for damage caused by the violence and injuries to police.
Folha de Sao Paulo reported that one of those taken into custody had been booked for attempted murder of the police colonel, who was later released from the hospital.
Dressed in black, their faces masked, heads covered with a handkerchief of T-shirt, Black Bloc anarchists have been a disruptive factor in a wave of protests that have hit Brazil since June.
Authorities said Black Bloc members "screamed at police and tried to get them to react violently." A group of vandals, some wearing black hoods, smashed store and bank windows and bank teller machines in a bus station in the centre of Sao Paulo.
A public bus was set on fire, and subway and bus ticket machines destroyed during the riot.
Police wielding clubs and shields in turn fired tear gas to disperse the mob.
The protest briefly blocked key city streets and disrupted the public transportation system in the city of 11 million.
Brazil is in the international spotlight as it prepares to host the World Cup next year and the Summer Olympics in 2016.
More than a million Brazilians took to the streets in June, angry at widespread corruption and the millions being spent on the sporting events.
Protesters say the money should instead be invested in improved transportation, education and health services.
In a June protest in Sao Paulo, tens of thousands marched over the poor condition of the public transportation system.
Smaller protests have since been taking place in Sao Paulo and Rio de Janeiro. Those protests are often led by radical groups and usually end up in clashes with police.
The Black Bloc, which first emerged in Germany in 1980, springs from a movement that unlike the radical left disdains institutions and political parties.
The group gained notoriety during violent street protests that accompanied the 1999 World Trade Organization summit in Seattle, seen as a key moment in the anti-globalization movement.