The state security service described the mass escape attempt as a military-style battle with inmates aided from outside.

Several inmates and one guard have died in an attempted prison breakout in the northern city Brazilian city of Belem.

The inmates were aided by an armed group on the outside who tried to blow up a wall on Tuesday, officials said.

A heavy gunfight erupted at the Santa Izabel Prison Complex outside Para’s state captial when the inmates and their supporters tried to stage the mass escape.

The state security service identified 19 of the dead as prisoners or their supporters at the Santa Izabel penitentiary. One guard was also killed.

At least four guards were injured, including one who was in serious condition.

The state security service said in a statement that “in the rescue attempt, explosives were used against one of the walls”.

The statement added: “The attempt was supported by an extremely heavily armed group. According to preliminary reports, the prisoners also had weapons inside the prison.”

A headcount was under way late on Tuesday to establish whether anyone escaped.

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According to the statement, the police had also recovered two rifles and five handguns at the scene.

Brazil has more than 726,000 prisoners in its notoriously violent and overcrowded prisons, which is more than the double of its total capacity of 368,000.

It is also one of the world’s deadliest countries, with about 60,000 homicides a year.

Last year, 56 people were killed in an uprising in the city of Manaus in Brazil’s Amazon.

In January of this year, fighting between gangs at a prison in the northeastern state of Ceara left 10 people dead.