A minimum of 64 civilians died in a security raid cracking down on the Red Command gang in Rio de Janeiro's north zone - the most extensive and fatal action in the region's history.
Four police officers were included in the fatalities during Operation Containment in the neighborhoods of Alemão and Penha, government representatives said. More than 80 suspects were taken into custody.
Violent conflicts broke out when around 2,500 law enforcement officers entered the area on Tuesday early hours. The criminal organization responded with shooting, igniting obstacles and launching explosives via unmanned aircraft, authorities confirmed.
The UN Human Rights Office expressed being "shocked" by the security action, urging "swift and comprehensive examinations".
The informal settlements close to Rio's airport is seen as the central command of a major criminal organizations.
Local authorities stated no less than 50 of the deceased were "identified by authorities as alleged offenders".
Many residents were injured, including civilians caught in the crossfire.
Residents have likened the hillside area - housing around 300,000 people - to a "combat area" since the operation began.
Access ways continue shut across the area.
The Comando Vermelho organization has been growing their control throughout the region, expanding narcotics distribution networks and control of the hillside favelas.
Security forces said over 200kg (441lb) of drugs were confiscated in the mission, together with multiple guns.
The joint operation by civil and military police follows a twelve-month inquiry.
Many of the individuals are considered affiliates of a group from the northern region who are at the moment taking refuge in the city.
Extensive security missions are not uncommon in the country before important worldwide conferences in the country.
The UN climate summit the climate conference is scheduled in the city of Belem in the north in the eleventh month.
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