A lot of prisoners are very frightened of the gang

The BBC's Tom Gibb

The PCC was protesting against a decision by the authorities to transfer 10 of its leaders from Carandiru prison in Sao Paulo to other prisons.

The proposed move followed accusations that the PCC was involved in the killing of five inmates last week.

''It was a carefully planned operation by an organisation that exerts its influence over inmates in other prisons,'' said Sao Paulo's public security secretary, Marco Vinicio Petreluzzi.

Corrupt guards

Human rights groups have long claimed that criminal groups like the PCC practically run Brazil's overcrowd prison system.

PCC gang has defied the authorities

PCC members keep in contact with mobile phones smuggled through heavy prison security with the help of corrupt guards.

With the phones, they continue to run their criminal activities outside prison.

Last week, the state secretary for prisons, Nagashi Furukawa, said he was searching for technology to block mobile phone signals inside prisons.

Induction ritual

The PCC was formed at a maximum security prison in northern Sao Paulo state in the 1990s and now has an estimated 1,500 members.

Prisoners are reportedly inducted into the gang in a ritual where they cut their fingers and promise to kidnap officials to back demands for shorter prison sentences.

Two weeks ago, men linked to the PCC were accused of kidnapping a prison director and seven members of his family to force the release of five inmates.

The BBC's Tom Gibb in Sao Paulo says gangs like the PCC have enormous power in Brazil's prisons.

''A lot of the prisoners are very frightened of it,'' he said. ''A lot of the prisoners who are not involved may themselves in many ways be hostages.''