Five people have died in a wave of violence in the Brazilian state of Sao Paulo where police stations, banks, shops and buses came under attack.
About 40 attacks were reported across the state
The unrest appears to be the latest development in an ongoing battle between the security forces and a powerful criminal gang, the PCC.
Authorities say the PCC was behind a series of attacks across Sao Paulo in May that led to more than 120 deaths.
The latest violence followed a large operation against the gang.
Officials say there were nearly 40 attacks in Sao Paulo state overnight and carrying on into Wednesday morning.
Among the dead were a policeman, his sister and two security guards.
Buses were set alight, two supermarkets ransacked, and several banks and car dealerships firebombed.
Notices were left at some of the scenes, condemning what was termed "oppression" in the Brazilian prison system
The Brazilian media has no doubt that the violence was ordered by the PCC, the First Command of the Capital, a criminal gang which is run in large part by its leaders from prison, the BBC's South America correspondent Daniel Schweimler reports.
The violence erupted shortly after a PCC leader, Emivaldo Silva Santos, was arrested.
Off-duty prison guards have been targeted over the last two weeks
Two months ago, gang violence erupted across Sao Paulo. The authorities blamed the unrest on the PCC which was angered by the transfer of its leaders to maximum security prisons.
About 40 police and prison guards were killed. The official number of people shot by police in response officially stands at 79.
The violence has continued, creating what our correspondent says is a climate of fear in Brazil's richest and most populous state.
Over the past fortnight, the PCC has been blamed for attacks on off-duty prison guards, who have been killed at the rate of one every 48 hours.
President Luiz Inacio Lula da Silva has again offered to send federal troops to help stem the violence, but so far the governor of Sao Paulo, Claudio Lembo, has declined.