A minimum of 64 civilians died in a security raid cracking down on the organized crime group in the Brazilian city's north zone - the largest and deadliest raid in the area's history.
Four security agents were included in the fatalities during the police action in the Alemão and Penha districts, government representatives said. Over 80 individuals were arrested.
Violent conflicts erupted when about 2,500 security personnel initiated the operation on the morning of the operation. The Red Command countered with armed resistance, igniting obstacles and using drone-dropped explosives, officials confirmed.
The United Nations human rights body stated it felt "appalled" by the law enforcement raid, urging "swift and comprehensive examinations".
The area of favelas adjacent to the city's international airport is seen as the headquarters of among the nation's strongest organised crime groups.
State officials confirmed at least 50 of those killed were "identified by authorities as alleged offenders".
Numerous individuals were wounded, including civilians caught in the crossfire.
Community members have compared the hillside area - home to about 300,000 residents - to a "battlefield" since the operation began.
Transport routes stay blocked across the area.
The Comando Vermelho organization have been expanding their territory across the Rio state, expanding narcotics distribution networks and control of the hillside favelas.
Local law enforcement said over 200kg (441lb) of drugs were captured in the operation, along with numerous weapons.
The joint operation by various security forces follows a year-long investigation.
Dozens of the suspects are thought to be affiliates of a group from the Brazilian state who are presently concealed in the city.
Large-scale police operations are not uncommon in Brazil ahead of major international events in the South American nation.
The UN climate summit the environmental summit is scheduled in the city of Belem in the north in the eleventh month.
Lena is a passionate gamer and tech writer, specializing in indie games and hardware reviews, with years of industry experience.