BELO HORIZONTE: Brazilian police fired tear gas Wednesday to disperse protesters near the stadium hosting a Confederations Cup football semi-final, with tens of thousands of people venting their anger.

The unrest outside the venue in Belo Horizonte, where Brazil beat Uruguay 2-1, was the latest in a wave of anti-government protests staged in part to denounce the high costs of hosting the event and next year's World Cup.

Some of the 40,000 demonstrators blocked five roads and set a bus ablaze in Brazil's third largest city, the capital of Minas Gerais state, ahead of the match.

Police fired tear gas to disperse a group of protesters who tried to remove metal barriers outside one of the access points leading to the Mineirao stadium.

Fourteen people were detained for carrying gas masks, stones, knives and sticks, police said.

Demonstrations were also planned in a dozen other cities, including Brasilia, where 2,000 people gathered outside the National Congress. Some 40,000 were expected to turn out. "We are putting pressure on the government and politicians and it worked," said Carolina de Moraes, a 17-year-old student.

The nationwide protests in Brazil initially focused on a hike in transport fares before mushrooming to encompass a variety of gripes including corruption and the lack of investment in health and education.

Brazil has spent $15 billion to stage the Confederations Cup and the World Cup -- a sum protesters say is way too high given the state of public services in the world's seventh largest economy.

As a sign authorities are listening to public complaints about corruption, the Supreme Court on Wednesday ordered the immediate detention of lawmaker Natan Donadon, who was sentenced to 13 years in jail in 2010 for embezzlement -- the first such move in 25 years.

In Brasilia, President Dilma Rousseff huddled with leaders of the country's leading unions, who vowed to maintain a "day of struggle" for July 11 even aftrer the talks.

The unions are calling for a shorter work day, a readjustment of pensions and bigger investments in health and education as demanded by the hundreds of thousands of Brazilians that have taken to the streets in recent days. "The July 11 mobilization is being maintained and we reaffirmed this to the president," said Carmen Foro, vice president of the Unified Workers' Central (CUT), Brazil's main national trade union. "This is not a general strike but there will be mobilizations throughout Brazil and also symbolic work stoppages," Foro added.

Rousseff meanwhile pressed on with her plans for a popular plebiscite on political reform to defuse public anger.

She has also proposed to earmark $25 billion for public transport and urged tougher penalties for those found guilty of corruption.

Rousseff dropped an earlier idea of holding a referendum on the creation of a constituent assembly on reform, in the face of strong protests from lawmakers and jurists.

The proposed plebiscite would be non-binding and allow for debate of several issues, while a referendum involves a popular vote which is binding on the government.

Officials said Rousseff would consult with parties allied to her ruling leftist Workers Party (PT) as well as the opposition to craft the questions on reform that will be included in the popular plebiscite. "There is a need in Brazil to include the people in the discussions on reforms. Brazil is tired of reforms that come from the top," Supreme Court chief Joaquim Barbosa said Tuesday after meeting with Rousseff.

Education Minister Aloizio Mercadante said all efforts would be made to hold the plebiscite as soon as possible, as presidential elections are scheduled for October next year.

The protesters scored a major victory Tuesday when Congress scrapped a proposed constitutional amendment that sought to curb the investigative powers of independent public prosecutors -- a key demand of the demonstrators.

Passage of the amendment would have made it harder to combat corruption. Paulo Pereira da Silva, president of the Forca Sindical union, said each labor federation would decide how to handle the July 11 actions. "For us it will be a day of mobilizations, but also of strikes. On Friday we are going to work out which sector can stop a day, an hour and stage demonstrations. We will hit the industrial and transport sectors," he told AFP.

CUT president Vagner Freitas said: "We want to back the demands by street protesters for public investments in health, education and transport... as well as for a reduction of the work day."

July 11 will mark the first time in more than 10 years that Brazilian labor unions are staging joint industrial action. (AFP)