At least 21 people have died since Sunday in a wave of drug violence and clashes between traffickers and police in Rio de Janeiro, authorities said.
On Wednesday alone, a massive police raid aimed at ending the attacks in the city left 13 dead, police spokesman Lima Castro said. Two police officers were injured.
The latest attacks have caused panic among residents. They were allegedly planned by two drug-trafficking gangs - Red Commando and Friends of Friends - which are trying to make the state government slowdown its policy of cracking down on drug dealers in the slums.
Castro said the involvement of the community was crucial in identifying the criminals linked to the attacks.
Governor Sergio Cabral asked Rio residents to stay calm and go about their daily business. "What criminals want is to generate panic and to make society backtrack," he said in a radio interview.
Cabral said the attacks represent "a desperate action, not a threat" from criminals, who he said have lost power because of the anti-drug policies, which include the occupation of 14 favelas or slums by police.
"They want to return to the crime-ridden situation in which they thrive. They are monsters, and big ones at that, and we are weakening that monster," Cabral said.
Rio is to host several matches of the 2014 football World Cup, while the city will single-handedly host the 2016 Olympics, the first-ever to held in South America.