Rio de Janeiro authorities say they are asking for 4,000 troops to help quell violence in the city's slums.
Some 1,200 armed police are already on patrol in the Rocinha slum
At least 10 people were killed in a shanty town at the weekend in a turf war among drug-trafficking gangs.
Rio's Public Security Secretary said the troops would patrol the Rocinha slum and other trouble spots until more police were recruited.
Drug-related killings in Brazil's shanty towns have given the country of the world's highest murder rates.
"It is an undeclared war," the Brazilian O Globo newspaper said on Wednesday.
More than 1,200 police officers have already been stationed in Rocinha, where violence erupted on Friday night.
The shootings seem to have been prompted by gang rivalries over some of the city's most lucrative cocaine distribution points.
Several bystanders were reported to be among the 10 people killed.
Calm has returned but some Rocinha's residents were pessimistic that it would last.
"These days have been a terrible experience, and people will remain afraid for a long time," said Antonio Trajano, a shop owner in the shantytown, according to the Associated Press.
Public Security Secretary Anthony Garotinho said he had requested at least 4,000 soldiers - preferably special forces or paratroopers - to maintain order until new police can be recruited and trained.
The state governor, Rosinha Matheus, is also reported to have asked for help from the armed forces, saying fighting the drugs trade is also the federal government's responsibility.
Brazil has one of the world's highest homicide rates
Troops were deployed in Rio in February 2003 during Carnival celebrations, following a similar wave of violence.
The government has not yet indicated whether it will provide soldiers.
In Rio, meanwhile, some commentators expressed cynicism about the scale of the request.
Unlike most shantytowns or "favelas", Rocinha is in a luxury beachside zone of the city - a tourist magnet - and some analysts suggested the violence might have come too close for comfort for Rio's wealthiest inhabitants.
"Drug gangs are almost always fighting for territory," Rubem Cesar Fernandes, president of the human rights
group Viva Rio, told AP.
"The difference is that this time it happened in slums which are part of the 'beautiful' side of