Hundreds of landless Brazilian farm workers have stormed a congressional building in the capital, Brasilia.
The protesters say land reform is too slow
The protesters, carrying sticks and farm tools, smashed windows, tables and doors, overturned a car and clashed with police and security guards.
Officials said about 500 people were arrested and more than 25 hurt,one seriously, in the violence.
Most of the protesters are thought to be members of a militant offshoot of Brazil's main landless movement.
The activists managed to force their way into an annexe of the lower house of Brazil's Congress in Brasilia.
They reached a room next to one of the two main debating chambers where a parliamentary session was taking place.
The protesters smashed furniture and windows, and destroyed a car that was being displayed as part of a prize draw for congressional staff.
The demonstrators said they had entered the building to demand an end to what they called slave labour and changes to Brazil's legislation to speed up land reform.
They said they had planned a peaceful protest but the police had attacked them.
Lula has promised to help farm workers get land
It is thought the protesters belong to the Movement for the Liberation of the Landless (MLST), a radical offshoot of Brazil's mainstream landless movement.
One of the MLST leaders, Bruno Maranhao, is also an executive member of the governing Workers Party.
That will prove embarrassing for President Luiz Inacio Lula da Silva, who is seeking re-election this year, the BBC's Steve Kingstone in Sao Paulo says.
In a statement, the president condemned the unrest as an act of vandalism against democracy.
The farm workers have traditionally backed President Lula whose party strongly supports land reform.
But the government has come in for criticism for doing too little to accelerate the process.
When he was elected in 2003, the president promised to buy disused land and redistribute it to poor families with no home of their own.
But the MST says the government has failed to live up to its election promises to find homes for 400,000 families by 2006.