A minimum of 64 civilians died in a police operation against the Red Command gang in Rio de Janeiro's northern districts - the most extensive and fatal action in the area's records.
Four police officers lost their lives during the police action in the neighborhoods of Alemão and Penha, state officials reported. Over 80 suspects were arrested.
Fierce clashes erupted when about 2,500 police forces moved in on the morning of the operation. The criminal organization reacted using shooting, setting fire to barriers and launching explosives via unmanned aircraft, police representatives confirmed.
The UN Human Rights Office expressed being "appalled" by the security action, demanding "immediate and thorough inquiries".
The informal settlements near the city's international airport is regarded as the main base of a major organised crime groups.
State officials said a minimum of 50 of the fatalities were "indicated by police as suspected of being criminals".
Dozens of people were hurt, including civilians caught in the crossfire.
Community members have described the hillside area - inhabited by approximately 300,000 people - to a "battlefield" since the operation began.
Transport routes stay blocked throughout the region.
The criminal network have been expanding their territory across the Rio state, expanding narcotics distribution networks and power in the informal settlements.
Local law enforcement stated more than 200kg (441lb) of narcotics were seized in the mission, along with multiple guns.
The coordinated mission by civil and military police comes after a twelve-month inquiry.
Dozens of the suspects are thought to be participants in an organization from the Pará state who are presently concealed in the metropolitan area.
Large-scale police operations are regular in the South American nation prior to significant global gatherings in the South American nation.
The United Nations climate conference the climate conference is set to occur in the northern city of Belem in late autumn.
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