Sao Paulo, Brazil ? A notorious criminal gang unleashed a second wave of attacks against police Sunday in Sao Paulo, bringing to at least 55 the number of people killed in what one official said was the deadliest assault of its kind in Brazil’s history.

Meanwhile, another 33 related prison rebellions also broke out on Sunday, bringing the number of penitentiary revolts across Sao Paulo state to 51 at the peak of the two-day uprising – more than one-third of Brazil’s 144 prisons. By late Sunday, rebellions continued at 41 prisons, and inmates were holding 229 prison guards hostage.

Enio Lucciola, spokesman for the Sao Paulo State Public Safety Department, said the attacks and prison rebellions, planned by the First Capital Command, known by its Portuguese initials PCC, “were the most vicious and deadliest attacks on public security forces that have ever taken place in Brazil.”

The attacks were in response to the transfer of eight imprisoned PCC leaders, a practice authorities use to sever prisoners’ ties to gang members outside prison.

Late Sunday evening, the Folha de Sao Paulo newspaper’s Web site reported the death toll had risen to 55 and that at least 10 public buses had been burned by bandits in the city of Sao Paulo. Folha Online said passengers were ordered out of the vehicles before bandits set them ablaze.