Sao Paulo, Brazil (CNN) -- Tanks, troops and police pushed through the streets of two shantytowns in northern Rio de Janeiro Sunday in a move to retake control of some of the city's most crime-ridden areas.
In the predawn operation, state authorities targeted the slums, or favelas, of Jacarezinho and Manguinhos with more than 2,000 military troops and police. They have a larger long-term goal: securing 40 slums before the World Cup in 2014, and keeping them safe for the Olympics two years later.
Police said they seized automatic weapons, guns and grenades and arrested dozens of people in a series of slum raids over the weekend.
There were no reports of deaths or injuries Sunday. On Saturday, police said five suspected drug dealers were killed during a slum raid.
Police have already taken over about 30 favelas since they began operations in 2008, but it's an uphill battle. About one-fifth of Rio's residents live in the city's 1,000 shantytowns, many of them perched on steep hills overlooking beachside condominiums.
Jacarezinho and Manguinhos are smaller favelas, far from tourist hotspots, but they became centers for organized crime and drug dealing after other slums were taken over by police.
Sunday's operation there stands in stark contrast to the invasion of the Alemao favela in 2010, when more than 30 people were killed in shootouts.
Police now announce days in advance when they're going to go into a community, to avoid major violence.
But critics say it simply gives criminals a chance to escape to another slum, or the suburbs.
Authorities said they planned to set up a "police pacification unit" in Manguinhos by December, and in Jacarezinho by January.
Three years ago, they took a similar approach in the notorious Cidade de Deus, or City of God, slum where military police backed by the army seized control from drug traffickers.
"They were abandoned for 40, 50 years," said Maj. Bruno Xavier of the police pacification unit there. "You can't recover that in three years."
But now, Xavier told CNN last month, they plan to prove to the slum's 40,000 residents that they're here to stay.