At least 64 individuals lost their lives in a law enforcement action against the Red Command gang in Rio de Janeiro's northern suburbs - the largest and deadliest raid in the Brazilian state's history.
Four security agents were included in the fatalities during the security mission in the communities of Alemão and Penha, government representatives reported. More than 80 people were arrested.
Fierce clashes commenced when approximately 2,500 police forces initiated the operation on Tuesday morning. The Red Command reacted using shooting, igniting obstacles and launching explosives via unmanned aircraft, police representatives said.
The International human rights organization said it was "horrified" by the law enforcement raid, urging "prompt and effective investigations".
The informal settlements close to Rio's airport is seen as the main base of among the nation's strongest illegal networks.
Local authorities confirmed a minimum of 50 of the deceased were "identified by authorities as alleged offenders".
Dozens of people were wounded, including innocent bystanders trapped in shooting.
Community members have likened the hillside area - inhabited by approximately 300,000 people - to a "combat area" since the mission commenced.
Roads remain closed in the entire neighborhood.
The criminal network have been expanding their control throughout the region, increasing drug trafficking routes and power in the informal settlements.
Security forces stated in excess of 200kg (441lb) of illegal substances were seized in the mission, along with multiple guns.
The combined action by civil and military police was preceded by a twelve-month inquiry.
Many of the individuals are believed to be affiliates of a group from the Brazilian state who are currently hiding in the city.
Extensive security missions are not uncommon in Brazil prior to significant global gatherings in the South American nation.
The international environmental meeting the climate conference is taking place in the city of Belem in the north in late autumn.
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