At least 64 individuals lost their lives in a police operation cracking down on the Red Command gang in Rio de Janeiro's north zone - the largest and deadliest raid in the area's records.
Four security agents lost their lives during the police action in the neighborhoods of Alemão and Penha, state officials reported. Over 80 people were arrested.
Violent conflicts erupted when around 2,500 police forces moved in on the morning of the operation. The Red Command countered with gunfire, burning barricades and launching explosives via unmanned aircraft, authorities confirmed.
The International human rights organization said it was "horrified" by the law enforcement raid, urging "prompt and effective investigations".
The area of favelas adjacent to Rio's airport is considered to be the headquarters of among the nation's strongest illegal networks.
Local authorities confirmed no less than 50 of those killed were "indicated by police as suspected of being criminals".
Numerous individuals were hurt, including non-combatants affected by the violence.
Residents have likened the hillside area - inhabited by approximately 300,000 people - to a "battlefield" since the operation began.
Access ways continue shut across the area.
The Comando Vermelho organization has been increasing their influence in the area, expanding narcotics distribution networks and dominance over the slum communities.
Local law enforcement stated over 200kg (441lb) of narcotics were captured in the mission, along with numerous weapons.
The joint operation by civil and military police comes after a twelve-month inquiry.
Numerous alleged criminals are believed to be participants in an organization from the Brazilian state who are at the moment taking refuge in Rio de Janeiro.
Extensive security missions are regular in Brazil before significant global gatherings in the nation.
The United Nations climate conference the climate conference is scheduled in the northern urban center in the eleventh month.