The army deployed 950 troops in the sprawling favela Rocinha after almost a week of intense gun battles between rival drug gangsters and the police.
In the past week, many criminals to have launched an effort to dominate the drug trade in the area, not far from some of the city’s most expensive real estate and few milles of the Rock in Rio Festival.
A widely circulated video showed gunmen in shorts firing machine guns, rifles and pistols in an alleyway. Fighting flared up on Friday morning and piles of garbage were set on fire on Rocinha streets
Schools, businesses and a major road tunnel was closed. Residents have been cowering indoors, exchanging information via social media and WhatsApp.
The outbreak of violence is happening in the midst of the Rock in Rio music festival at the far south end of the city, which has drawn thousands of people with musical acts including Fergie and Aerosmith.
Broadcaster GloboNews on Friday showed relatively calm scenes of matte green military trucks filing down roads into the favela, including soldiers riding on trucks and motorcycles holding assault rifles.
There are up to 10,000 troops in Rio de Janeiro who could be mobilized if needed, the defense ministry said.