Gangsters armed with grenades and machine-guns have killed 52 people – mostly police officers and prison guards – in two nights of violence in Brazil's Sao Paulo state.
The violence, which police blamed on a gang called "First Command of the Capital" (PCC in Portuguese), began Friday night and continued into early Sunday morning.
The gang was responding to a government decision to move hundreds of prisoners – including PCC boss Marcos Willians Herbas Camacho, known as "Marcola" – to a new jail 620 kilometres from the capital, Sao Paulo city.
The inmates were being moved to prevent co-ordinated prison rebellions that officials believed were set for this weekend.
Riots break out in 36 jails
By Sunday morning, 35 officials, three civilians and 14 gangsters had died in 100 attacks and riots in 36 jails, the state security office said.
At least 53 people have been wounded.
"We are all indignant and in a state of mourning," said Sao Paulo Mayor Gilberto Kassab, who predicted the government would win the battle.
Sao Paulo has 20 million residents, making it the third-biggest city in the world.
It is notorious for crime, especially drug dealing, and the gangs are reputed to have close ties with corrupt police officers.