A police operation targeting Rio de Janeiro's favelas (slums) has left at least 18 people dead in one of the deadliest raids the city has seen in recent memory, AP reported.

Authorities in Rio said 16 suspected criminals, as well as a policeman and a woman, were killed in clashes with police in Complexo do Alemão. A police spokesman said the target of the raid was a criminal gang that was stealing cars and robbing banks, as well as invading nearby neighborhoods.

Videos circulating on social media show fierce gunfire, as well as a police helicopter flying low over small brick houses. Rio de Janeiro police used helicopters to shoot at targets even in densely populated residential areas.

According to locals, those who tried to help the victims faced arrest. “It's a massacre inside, which police are calling an operation,” one woman told Associated Press, speaking on the condition of anonymity. “They’re not letting us help (victims),” she added, saying she saw one man arrested for attempting to do so.

A Rio de Janeiro police spokesman said some of the perpetrators wore uniforms to disguise themselves as police officers.

Many people disagree with the government's strategy to combat violence and organized crime, which regularly results in deadly police operations. A raid in Rio's Vila Cruzeiro favela in May killed more than 20 people.