Gunmen sprayed police stations with bullets before dawn Sunday in the latest eruption of gang violence, but authorities insisted they were restoring order ahead of a huge New Year's Eve bash on Copacabana beach.
Also on Sunday, suspected gang members hurled grenades at a firefighters' station, according to Agencia Brasil, the nation's official news agency.
No one was killed or hurt in Sunday's attacks, Brazilian media said, quoting authorities who cited that as evidence that they were regaining control of the city.
The attacks came three days after a wave of assaults by suspected gang members left 19 dead, including eight killed after the bus they were riding was set ablaze.
Nearly 21,000 police officers fanned out across the city, many of them patrolling Rio slums where gangs rule neighborhoods and can be better armed than authorities. On Saturday, officers killed 6 suspected gang members in shootouts, but it was not clear whether those who died had any links to the initial violence outbreak.