Protesters on Friday promised more organized action across Brazil in the days to come, following clashes in which police in Sao Paulo set upon thousands of young demonstrators angered by hikes in bus and subway fares.

Newspapers carried photos of bloodied protesters and journalists with battered, swollen faces, a young couple being beaten by police and videos of tear gas canisters and rubber bullets being fired into crowds chanting "no violence!" Protesters set fire to garbage bags piled in streets, broke windows and spray-painted graffiti on buildings and buses.

More than 100 protesters and 12 police were injured and over 230 people detained and later released in the Thursday night demonstrations in Sao Paulo.

Similar protests were seen in Rio de Janeiro, the capital Brasilia and in Porte Alegre in southern Brazil. The conflicts come just as the Confederations Cup football tournament opens and the nation prepares to host Pope Francis next month on his first international trip as pontiff.

Since the end of the 1964-85 military dictatorship, Brazil has witnessed few protests as violent as those in recent days. The focus of the protests is a 10-cent hike in public transport fares.

Protesters said that seemingly small increase released pent-up frustrations in a nation with a heavy tax burden yet woeful public education, health and transport systems.

"It's about much more than those 10 cents. It's about a society that is sick of corrupt politicians not making good on their promises to make improvements," said Bruno Bisaglia, 24, who was gathering video testimony about the protests. "We want decent education, health care and transportation. That's what this fight is all about."

Sao Paulo Mayor Fernando Haddad, whose office doesn't have responsibility over police, said individual officers "must be investigated" for using excessive force.

"Police always follow protocols. When these are followed, things go smoothly," Haddad told Globo TV. "But, according to images divulged by the press, the police yesterday apparently did not follow protocols, which is why the Public Safety department has ordered an investigation."

Sao Paulo state Gov. Geraldo Alckmin, who does have authority over police, told Globo an investigation is under way.

But he defended the officers, saying that "police are obliged to protect the population and guarantee the right to come and go. We are always open to dialogue ... but will never tolerate vandalism."

Alckmin said the government has invited protest leaders to talks on their demands, but that the protesters "don't want dialogue, they prefer monologues."

Police Col. Reinaldo Simoes Rossi, responsible for the officers policing the protest in Sao Paulo, said force was used only after demonstrators had altered an agreed upon route they marched along, instead moving toward main avenues in an attempt to halt traffic. He also said protesters hurled stones and other objects at police.

"The police guarantee the right to demonstrate, however it must also ensure the rights of the entire population, including the right to come and go. Any statements to the effect that police encouraged violence are completely unfounded," the police department said in a Friday statement.

In the nation's capital, Brasilia, about 200 people burned tires and blocked the main road in front of the city's football stadium, which will host the Confederations Cup opener on Saturday.

The protest was organized by local groups complaining of excessive costs of the Confederations Cup and the World Cup. A black cloud of smoke rose up near the stadium as protesters held aloft banners criticizing the local government.

The road they had blocked was opened again in the early afternoon.

Back in Sao Paulo, secretary Dionizia Aragao, 40, lamented the rise in bus fare, noting that her commute eats up nearly 10 percent of her monthly salary of $350.

"I don't agree with violent protests, but people are fed up with low-quality public transportation that comes at a high price," she said while waiting at a bus stop on Sao Paulo's main business thoroughfare, Avenida Paulista. "The anger will remain until improvements are made."


Associated Press writers Stan Lehman in Sao Paulo and Tales Azzoni in Brasilia contributed to this report.