Brazilian President Dilma Rousseff is battling to calm the country's educational institutions after thousands of sympathizers from other sectors joined protests by teachers.

Street riots in Rio de Janeiro and Sao Paulo earlier in the week left tens of thousands of dollars in damage, wrecking urban landscapes just when authorities are trying to spruce up Brazil's image before next year's FIFA World Cup.

Riots by dozens of homeless and unemployed protesters in other locations also led to angry encounters between crowds and police. Cars, buses, telephone kiosks and shops were attacked and some vehicles and establishments were torched.

Arrests and casualties among protesters and police, reported in varying numbers by Brazilian news media, were not discussed in police statements. Dozens were detained after each protest, Brazilian media reported.

In parts of Brazil, the protests were compounded by strikes by oil industry workers.

The teachers want better pay and living allowances, the homeless want accommodation and financial support, and the oil workers want higher wages and guarantees against foreign companies' participation in Brazil's oil boom. Critics say the government is failing to ease poverty and income disparities, claims contested by senior officials.

Recent police and army crackdowns on urban favela slums have increased homelessness and disrupted communities, critics say.

Government agencies received orders last year to spare no effort in cleaning up Brazilian cities and removing what officials condemn as the shameful blight of slums set against neighborhoods of middle- to high-income affluence.

More than 5,000 protesters filled the streets in Rio de Janeiro. In previous protests the numbers swelled to 10,000 or more at a time.

Most protests started without major incidents, but tempers soon flared, splinter groups branched out to confront the police and lob petrol bombs at law enforcement units. Several police cars were set on fire or damaged in separate clashes.

Rioters in Sao Paulo vented fury at banks and trashed at least seven financial establishments, local news media reported.

Both police and protest groups say most of the violence is the work of the anarchist Black Bloc, which targeted street installations and public amenities, including advertising signs and telephone kiosks.

Teachers' protests have been simmering in Brazil for more than two months and some have been exacerbated by a tough government response, including punitive measures. Protesters say officials have made no attempt to talk about a resolution of their grievances. Some teacher groups got support from judicial figures but noted it was not vocal enough to be effective.

Judge Luiz Fux, cited in Agencia Brasil dispatches, called sanctions on teachers illegal and a challenge to their right of freedom of expression.

Protests also took place in the southeastern city of Belo Horizonte, Salvador in the northeast, Brasilia and other towns.

Analysts said the teachers' anger at a lack of government response threatened to mix with rising unrest among oil workers protesting a planned international auction of rights to the offshore Libra oil field.

At least 42 platforms and several refineries have been affected by the oil workers' action.

Union leaders say the Libra oilfield auction will undermine their interests as it will lead to the entry of foreign companies in an industry dominated by Petrobras state oil company. About 40,000 Petrobras employees want pay raises and oppose plans to contract out some services to private companies.