Rio de Janeiro's state governor headed to Brasilia on Friday to seek help from the government in a bid to stamp out a surge in slum violence ahead of the World Cup.
A series of attacks on police units in Rio's sprawling favelas have raised alarms among state security officials, less than three months before the World Cup kicks off.
"It is clear that criminals want to weaken our policy of pacification and take back territories which were in criminal hands for decades," Rio state governor Sergio Cabral said. "The state will not back down. The public may be sure we shall act, " he vowed.
Looking to clean up the city's violent image, Rio authorities have installed 38 so-called Police Pacification Units (UPPs) in favelas to drive out drug gangs that had turned them into no-man's lands.
Seven World Cub matches, including the July 13 final, are to be played in Rio.
The city also is in the world spotlight as host of the 2016 Summer Olympics, the first ever held in South America.
But attacks on police have intensified in recent weeks, with three more reported Thursday night, including in the larger northern favela known as Complexo de Alemao.
Police Colonel Frederico Caldas later revealed that five of seven police units in the Mandela favela within Rio's northern Manguinhos district were attacked overnight, with two police cars torched.
"Five of seven units (in the sector) were set ablaze -- these are organized attacks," local UPP head Caldas told broadcaster Globonews.
In 2010, the armed forces were brought in to retake Complexo de Alemao from drug gangs, with police being left to hold it.
Cabral, who traveled to Brasilia with his top security officials for the meeting with the president, said he would ask Rousseff for help from the federal police, a government spokesman told AFP.