Demonstrators in Paraguay have set fire to the country's parliament during violent protests against a bill that would lift presidential term limits.
One activist was killed by a blow to the head which the opposition blamed on a rubber bullet fired by police.
Under the 1992 constitution, introduced after the dictatorship, a head of state may only serve a single five-year term.
But sitting President Horacio Cartes is trying to remove the restriction and run for re-election.
Protesters were photographed smashing in windows of the congress building in the capital, Asuncion, on Friday night and setting fire to the interior.
Protesters "ransacked" the offices of those who had backed the bill, AFP news agency reports.
Police used rubber bullets, mounted units and water cannons to disperse the crowd. A number of people were injured, with AFP saying about 30 had been hurt, including three lawmakers and a senator.
Santi Carneri, a journalist in Asuncion, told the BBC the congress building had burnt for "more than one or two hours".
There were "a lot of battles between people and the police in the streets", he said, adding that it was the worst violence of its kind since Paraguay became a democracy in 1992.
Opposition activist Rodrigo Quintana, 25, was killed by a rubber bullet fired by police when they stormed the offices of the opposition Liberal party, party leader Efrain Alegre told Efe news agency.
"The police barged in, threw people face down to the ground," according to Mr Alegre, who was also hurt. "They came in aggressively, breaking the doors, it was savagery."
Herminio Ruiz, the doctor who treated Mr Quintana, told Efe the victim had received a blow to his head, although did not specify what had caused the injury.
Police have launched an inquiry into the circumstances surrounding his death.
In a statement released on Twitter, President Cartes appealed for calm.
"Democracy is not conquered or defended with violence and you can be sure this government will continue to put its best effort into maintaining order in the republic," he said (in Spanish).
The protesters had taken to the streets following a private meeting of 25 senators - a slight majority of the house - which approved a bill to amend the constitution.
The bill must also be approved by the other house of parliament - the chamber of deputies - where President Cartes' party holds a majority.
The chamber's president, Hugo Velázquez, told ABC Color (in Spanish) that the sitting planned for the following morning would no longer take place and no decision would be made on Saturday.
Opponents say the bill will weaken the country's democratic institutions.
Opposition senator Desiree Masi said: "A coup has been carried out. We will resist and we invite the people to resist with us."
Paraguay was controlled by military ruler General Alfredo Stroessner, who seized power in a coup, from 1954 until 1989.
The new constitution in 1992 created the modern government but there has been a long period of political instability and party infighting, as well as a failed coup attempt.
President Cartes' term is due to end in 2018.
The change, if approved, would also allow former President Fernando Lugo to run again.
Mr Lugo was ousted in 2012 over his handling of a land eviction in which 17 people were killed. His supporters would like to see him run again.