At least 64 civilians lost their lives in a police operation cracking down on the Red Command gang in the Brazilian city's north zone - the biggest and most lethal operation in the region's history.
Four security agents were included in the fatalities during the security mission in the neighborhoods of Alemão and Penha, state officials reported. In excess of 80 suspects were arrested.
Intense confrontations erupted when approximately 2,500 law enforcement officers entered the area on Tuesday morning. The Red Command countered with gunfire, setting fire to barriers and launching explosives via unmanned aircraft, authorities stated.
The International human rights organization said it was "appalled" by the security action, urging "swift and comprehensive examinations".
The area of favelas near Rio's airport is seen as the main base of one of Brazil's most powerful criminal organizations.
Local authorities confirmed a minimum of 50 of the fatalities were "classified by law enforcement as potential lawbreakers".
Numerous individuals were wounded, including civilians caught in the crossfire.
Locals have compared the hillside area - home to about 300,000 residents - to a "war zone" since the mission commenced.
Access ways continue shut in the entire neighborhood.
The criminal network have been expanding their control throughout the region, expanding narcotics distribution networks and control of the hillside favelas.
Local law enforcement said over 200kg (441lb) of illegal substances were captured in the raid, in addition to dozens of firearms.
The coordinated mission by civil and military police follows a year-long investigation.
Many of the individuals are thought to be members of a faction from the Pará state who are presently concealed in Rio de Janeiro.
Extensive security missions are frequent in the country prior to significant global gatherings in the nation.
The UN climate summit the climate conference is scheduled in the northern urban center in the eleventh month.
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