At least 64 people, including four police officers, were killed and another 81 arrested during a large-scale operation Tuesday against the criminal organization Comando Vermelho (or “Red Command”) in the northern Alemao and Penha neighborhoods of the State Rio de Janeiro, Brazil, G1 reports.

Police seized around 100 automatic rifles. This is the bloodiest operation in the state’s history, as confirmed by the government of Rio (Guanabara Palace).

Rio de Janeiro Governor Claudio Castro announced in the evening that the operation had no specific end date.

Around 6:30 p.m. local time, intense gunfire was again heard in the area. In response to police actions, drug traffickers launched counterattacks throughout the city, plunging Rio into hours of tension and chaos reminiscent of war.

The aforesaid operation is part of an ongoing initiative called “Operation Containment,” aimed at countering the expansion of Comando Vermelho’s influence in Rio de Janeiro’s suburbs and communities.