Relatives of inmates react in front of a prison complex in the Brazilian state of Amazonas after prisoners were found strangled to death in four separate jails, according to the penitentiary department in Manaus. Nine inmates suspected of ordering the killing of 55 prisoners in northern Brazil in the past two days will be transferred to federal jails, officials said on Tuesday. File photo: REUTERS/Bruno Kelly.

Sao Paulo - Nine inmates suspected of ordering the killing of 55 prisoners in northern Brazil in the past two days will be transferred to federal jails, officials said Tuesday. 

Most of the victims killed Sunday and Monday in four Amazonas state prisons died from "asphyxiation", officials said, in the latest violence to erupt in Brazil's overcrowded and deadly penitentiary system. 

"We are going to free up spaces in our federal prisons for the leaders involved in these massacres," justice minister Sergio Moro said on Twitter. 

Around 100 federal troops are being deployed to reinforce security at the prisons, state governor Wilson Lima told reporters. 

Fifteen inmates were killed during visiting hours at the Anisio Jobim Penal Complex on Sunday. Some were stabbed with sharpened toothbrushes.

The following day 40 inmates were found dead in four prisons, including Anisio Jobim. 

No guns or knives were used in Monday's killings, which prison officials said appeared to have been sparked by a "rift between prisoners who belonged to the same criminal group and were involved in drug trafficking in the state."

Experts warned the deaths could trigger payback killings inside and outside the prisons in Amazonas, one of Brazil's most violent states. 

Brazil has the world's third largest prison population after the United States and China, with more than 726,000 inmates as of June 2016 -- double the capacity of the nation's jails, according to official statistics.

Along with severe overcrowding and gang violence, riots and breakout attempts in Brazil's prisons are not uncommon.

Authorities have little control over many prisons, which are often ruled by drug trafficking gangs who serve as "judges, jurors and executioners", said Robert Muggah, research director at the Igarape Institute think tank in Rio de Janeiro.

AFP