Police have fired rubber bullets and tear gas at about 16,000 landless farmers marching for land reform in clashes that left 42 people hurt.
Wednesday’s march in the capital Brazilia was the latest in a series of protests rocking the nation, raising security concerns just four months before Brazil hosts football’s World Cup.
After a peaceful beginning, protesters clashed with police as they neared the presidential palace and began to dismantle barricades.
President Dilma Rousseff was not in the building as the disturbance unfolded.
A spokesman for the marchers told AFP that police moved in after some demonstrators began to erect a barricade of tents.
In the end, 30 police were injured – as well as 12 of the protesters, police and the Landless Movement (MST) said.
A protest in Rio de Janeiro on Thursday ended in tragedy when TV cameraman Santiago Andrade was struck on the head by a flare thrown by a demonstrator, and died of his injuries four days later.
A 23-year-old man suspected of throwing the flare was arrested in northern Brazil. He faces up to 35 years in prison.
This year has seen sporadic demonstrations in Brazil, while the burning of buses in business hub Sao Paulo has become an almost daily occurrence.
Last week’s unrest in Rio was sparked by the latest rise in transport fares, the same issue that prompted nationwide demonstrations in June.
Protests since then have been smaller but more radical as anarchist groups have infiltrated them. Police have responded, sometimes in heavy-handed fashion.
Brazilians are angered by poor public services while their country spends billions of dollars to host the World Cup and the Rio Olympics in 2016.
Wednesday’s marchers in Brasilia comprised agricultural workers marking 30 years of the MST movement whose previous marches had been peaceful.
Across the square from the protest, Brazil’s Supreme Court suspended its session owing to the size of the protest.
The marchers dispersed shortly after the clash with police.
Many grumbled that Rousseff, though a leftist, is allowing agro-business to undercut chances of land reform instead of worrying about them.
The landless movement has spent decades demanding wide-ranging land reform but frustration has grown at the slow progress being made.
Born in 1984 in the final days of two decades of military dictatorship, the MST has become Brazil’s main organised social movement, helping some 350,000 families obtain land.