A minimum of 64 civilians lost their lives in a law enforcement action cracking down on the Red Command gang in the Brazilian city's northern districts - the biggest and most lethal operation in the region's past.
Four security agents were included in the fatalities during Operation Containment in the Alemão and Penha districts, government representatives stated. Over 80 individuals were detained.
Violent conflicts erupted when about 2,500 security personnel entered the area on the morning of the operation. The Red Command responded with gunfire, burning barricades and launching explosives via unmanned aircraft, officials said.
The UN Human Rights Office stated it felt "horrified" by the law enforcement raid, urging "immediate and thorough inquiries".
The slum neighborhoods adjacent to the aerial transportation hub is regarded as the central command of one of Brazil's most powerful illegal networks.
Local authorities said no less than 50 of the deceased were "indicated by police as suspected of being criminals".
Dozens of people were injured, including civilians caught in the crossfire.
Community members have likened the hillside area - inhabited by approximately 300,000 individuals - to a "battlefield" since the mission commenced.
Access ways continue shut in the entire neighborhood.
The Red Command group has been growing their control throughout the region, growing illegal substance trade paths and control of the hillside favelas.
Local law enforcement reported more than 200kg (441lb) of narcotics were seized in the raid, together with multiple guns.
The combined action by various security forces follows a year-long investigation.
Many of the individuals are believed to be participants in an organization from the Pará state who are currently hiding in the metropolitan area.
Major law enforcement actions are regular in the South American nation ahead of major international events in the South American nation.
The United Nations climate conference the climate conference is set to occur in the city of Belem in the north in late autumn.
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