Hundreds of Brazilian police officers backed by armoured cars and helicopters have moved to take control of two Rio de Janeiro slums notorious for drugs.
Some 1,500 police and commandos took part in the operation in the northern favelas of Jacarezinho and Manguinhos, which began at 05:00 (08:00 GMT).
The no-go areas are known as centres for the trafficking of crack cocaine.
Brazil has been trying to clean up its most dangerous regions ahead of the 2014 World Cup and 2016 Olympics.
The raids are part of a policy known as "pacification" which was adopted in recent years to help the state establish a more permanent presence in shanty towns.
The drug gangs' gunmen apparently retreated ahead of the operation and there appeared to be little resistance.
Brazil is the world's largest consumer of crack cocaine, and the second largest consumer of cocaine and derivative drugs after the US, according to a study released last month by the Sao Paulo Federal University.
Up to 2,000 police, including elite forces supported by soldiers from the Brazilian navy, took part in the operation backed by armoured vehicles and helicopters.
Moving in groups of eight, police made their way through the alleys of Jacarezinho, searching houses, while armoured cars took up position beside rubbish dumps, news agency AFP reported.
Some residents of the favela could be seen looking out of their windows at the advancing police, while others broke down in tears when their homes were searched.
BBC Brasil's Julia Carneiro says that police have "pacified" more than 20 shanty towns in recent years.
The policy represents a shift in strategy for authorities in the city, she says.
In the past police units would enter favelas and engage in gun battles with drug gangs before making arrests and then leaving the area, which could result in the deaths of civilians who had nothing to do with drug trafficking.
The policy of pacification has been praised for establishing state control in areas that were previously controlled by heavily armed drug traffickers, but in some areas people have complained of police violence and corruption.
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