Rio's slums have become centres of violence and criminal activity
Military police in Brazil are carrying out a manhunt in several slums in Rio de Janeiro to find the gunmen who shot down a police helicopter on Saturday.
Three policemen were killed in the attack, which led to two days of violence that left 21 people dead.
The violence has sparked renewed concerns over Rio's preparedness to host the Olympic Games in 2016.
Earlier, Brazil's president pledged to do everything to combat gang warfare, which has spiralled out of control.
"We will do anything it takes and make all necessary sacrifices so we can clean up the mess that these people are imposing on Brazil," President Luiz Inacio Lula da Silva told reporters in Sao Paulo.
"When you have a conflict of this magnitude, the innocent people always pay the price."
President Lula also promised that the federal government would provide an additional $58m (£35m) to deal with the violence and provide the police with a bulletproof helicopter.
Saturday's attack on the police helicopter, which came down and burst into flames after the pilot was hit in the leg by a bullet, followed an outbreak of fighting between rival drug gangs.
Several buses were also set on fire during the worst outbreak of violence since the city was awarded the Games two weeks ago.