Prisoners complaining of violence behind bars ordered a wave of attacks out on the streets in southern Brazil over the past two weeks, officials said Friday as police reinforcements began arriving.
The state of Santa Catarina has seen buses torched and police fired on in some 30 cities since January 30.
Authorities say the violence has been masterminded by prison-based crime gangs demanding better living conditions for inmates.
"What the investigation shows is that the attacks were triggered by problems within the prison system. Inmates claimed they were the victims of violence and this is being investigated," said Claudete Lehmkuhl, a spokeswoman for the Santa Catarina military police.
"Prison guards have been dismissed and new measures could be taken," she added, citing the possible transfer of prisoners to other penitentiaries.
Prison-based gangs also control drug trafficking networks, Lehmkuhl added.
Press reports have blamed a gang called the First Group of the Capital, similar to a Sao Paulo-based prison syndicate known as the PCC, or First Command of the Capital.
The PCC was allegedly involved in various attacks and clashes with police that claimed more than 300 lives in and around Sao Paulo between October and early December.
Santa Catarina also witnessed an outbreak of criminal violence in November.
One person has been killed and 36 others arrested in the latest wave of assaults, most of them in Florianopolis, the state capital, where bus companies have decided to suspend service at night.