At least 64 people were killed in a police operation against the Red Command gang in Rio de Janeiro's northern suburbs - the largest and deadliest raid in the Brazilian state's history.

Four police officers were among those killed during Operation Containment in the Alemão and Penha districts, state Governor Cláudio Castro said. More than 80 people were arrested.

Fierce clashes erupted when about 2,500 security personnel moved in on Tuesday morning. The Red Command (Comando Vermelho) responded with gunfire, burning barricades and dropping bombs from drones, officials said. 

The UN Human Rights Office said it was "horrified" by the police operation, urging "prompt and effective investigations".

The area of favelas near Rio's airport is considered to be the headquarters of one of Brazil's most powerful organised crime groups.

State officials said at least 50 of those killed were "indicated by police as suspected of being criminals".

Dozens of people were injured, including civilians caught in the crossfire.

| Reuters (Pic): Some 2,500 security personnel took part in Tuesday's operation

Locals have likened the hillside area - home to about 300,000 people - to a "war zone" since the operation began.

Roads remain closed throughout the region.

The Red Command group have been expanding their territory across the Rio state, increasing drug trafficking routes and control of the hillside favelas.

Rio's police said more than 200kg (441lb) of drugs were seized in the raid, along with dozens of firearms.

The joint operation by civil and military police comes after a year-long investigation.

Dozens of the suspects are thought to be members of a faction from the Pará state who are currently hiding in Rio de Janeiro.

Large-scale police operations are not uncommon in Brazil ahead of major international events in the South American nation. 

The UN climate summit COP30 is taking place in the northern city of Belem in November.