Brazilian police say 12 people have been killed, including an officer and a four-year-old boy, during a raid on drug gangs in western Rio de Janeiro shanty towns.

Three officers were wounded when about 500 police officers backed by helicopters and armed vehicles confronted alleged traffickers in the Coreira and Senador Camara slums, police said.

Eleven arrests were made and five rifles, a machine gun, four hand grenades and unspecified quantities of cocaine and marijuana were confiscated.

Since being elected to office in January, Rio governor Sergio Cabral has pledged a relentless crackdown on drug gangs and their control over Rio‘s many slums, known as favelas.

Rio is one of the world’s most violent cities, with an annual murder rate of about 50 killed per 100,000 inhabitants.