Roughly 10,000 troops are being deployed in Rio de Janeiro as the state grapples with violent crime.
Brazil's President Michel Temer ordered the operation on Friday, saying soldiers are needed "to defend the integrity of the population."
The BBC notes over 90 police officers have been killed in the state so far this year. Through June, an average of three people a day were killed in the state by stray bullets.
Gunfights between police and drug traffickers have been a major source of violence. Brazil's defense minister said the troops will be taking an active role in shutting down traffickers' operations.
The operation in Rio state is expected to continue through the end of next year.
