No less than 64 people lost their lives in a law enforcement action cracking down on the criminal organization Comando Vermelho in Rio de Janeiro's northern districts - the largest and deadliest raid in the area's records.
Four security agents lost their lives during the police action in the Alemão and Penha districts, state officials said. More than 80 individuals were taken into custody.
Intense confrontations erupted when approximately 2,500 law enforcement officers initiated the operation on the morning of the operation. The Red Command countered with armed resistance, setting fire to barriers and dropping bombs from drones, officials stated.
The United Nations human rights body stated it felt "appalled" by the law enforcement raid, urging "prompt and effective investigations".
The slum neighborhoods near the city's international airport is seen as the headquarters of one of Brazil's most powerful organised crime groups.
Local authorities said at least 50 of the fatalities were "identified by authorities as alleged offenders".
Numerous individuals were hurt, including innocent bystanders trapped in shooting.
Residents have described the mountainous region - housing around 300,000 residents - to a "combat area" since the mission commenced.
Transport routes stay blocked across the area.
The criminal network has been increasing their territory across the Rio state, increasing drug trafficking routes and dominance over the slum communities.
Local law enforcement stated over 200kg (441lb) of drugs were captured in the operation, along with numerous weapons.
The coordinated mission by various security forces follows a year-long investigation.
Many of the individuals are considered affiliates of a group from the Brazilian state who are presently concealed in the metropolitan area.
Extensive security missions are regular in Brazil before important worldwide conferences in the country.
The UN climate summit the environmental summit is set to occur in the city of Belem in the north in late autumn.
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