Brazilian reconnaissance troops entered a sprawling slum district near Rio's international airport early Wednesday ahead of a larger operation to secure the crime-ridden area ahead of the World Cup.
The federal troops joined police in the deployment in Mare to set the stage for a major joint drive to "pacify" a cluster of 16 neighborhoods home to around 130,000 people and seen as havens for organized crime.
The Rio state government meanwhile announced the arrest of a man suspected of being a drug kingpin in Mare. It said he went by the nickname Menor P., and that he was also wanted for homicide and torture.
Rio authorities last week asked the government to approve military support for police in favelas after a series of attacks on police units.
Authorities are stepping up efforts to quell the violence as the World Cup, which kicks off on June 12, looms ever closer.
Rio will stage seven matches, including the July 13 final.
President Dilma Rousseff on Monday confirmed the government would send troop support following an appeal for assistance by Rio governor Sergio Cabral.
After decades battling organized crime in the favelas, the poor communities surrounding the city, authorities in 2008 launched a huge slum "pacification" program.
Since then, 38 Police Pacification Units (UPPs) comprising 9,500 officers have been installed in 174 favelas home to some 600,000 people.
But this year, renewed violence has claimed the lives of eight police officers — four of them in "pacified" districts.
Keeping a lid on crime has become key to Rio's bid to turn the city into an international showcase for the World Cup and the Rio Olympics in 2016, the first Olympiad in South America.
Police have been drawing up a map of the Mare suburbs to pinpoint areas where rival groups of drug traffickers have clashed.
Part of the military's role is to uncover traffickers' arms stashes, according to Globo daily.
Cabral last week said "there are weapons, drugs, stolen cars and motorbikes and criminals taking refuge" in Mare and using it "as if it were their territory."
He said that the much-postponed but now pending occupation of the favela "is a decisive step in our security policy."
It is not yet clear how many troops and police will go into the area nor exactly when the main force will deploy, though the operation is expected to take place early next month.
'Show of force'
Authorities say the troops will stay in Mare for as long as necessary prior to the installation of a 39th UPP.
The military occupation will be similar to that effected in 2010 in the Alemao network of favelas, home to about 300,000 people.
Alemao was occupied a week after 35 people had died in bloody clashes between police and drug dealers.
"The federal government supports the Rio government in this confrontation with organized crime," Justice Minister Jose Eduardo Cardozo said earlier this week.
"The Mare favelas are a priority," he added.
Michel Misse, an expert on urban violence at Rio's federal University, said earlier that bringing in the army "does not signify a failure of local police."
"Mare is a very complicated group of favelas, as is Alemao, where the military were also deployed.
"It is also a demonstration of force to reduce the risk to police, a symbolic aspect to show the force of the state against criminals," said Misse.
Rio state secretary for security affairs Jose Mariano Beltrame insisted Monday that authorities "are not thinking about the World Cup so much as the citizens of Rio, of police gunned down in cowardly fashion" on the streets.
"Our response to the traffickers is to occupy more territory, to make them lose more territory" and show the state is stronger than the dealers.
Rio state security secretary Jose Mariano Beltrame said the suspected Mare drug lord arrested is named Marcelo Santos das Fores.
Press reports said he has a reputation for extreme violence, cutting up the bodies of rivals. He was arrested in an apartment in the west of Rio.