Thousands of soldiers in armored vehicles, trucks and on foot fanned out in Rio de Janeiro's most notorious slums on Saturday to shore up security before the start of the World Cup games.

The move is the latest attempt to drive drug gangs out of the notorious Mare shanty town, a haven for organized crime and one of the city's most dangerous neighborhoods, located near Rio de Janeiro's international airport.

The Mare complex, home to 130,000 people, is a potential through route for tens of thousands of football fans flying in and out of the metropolis, which will stage seven World Cup matches, including the July 13 final.

Members of the feared Special Police Operations Battalion, with guns at the ready and backed by helicopters and naval armored vehicles, had stormed into the Mare favela on March 30.

However the entry was peaceful on Saturday, when some 2,700 soldiers, sailors and military police entered the slum at 6 am (0900 GMT).

Officials said their goal was to provide long-term security ahead of the start of the tournament. Brazil will face Croatia a little more than two months from now, in the World Cup curtain-raiser on June 12.

Residents went about their business during the crackdown, occasionally poking their heads out of windows to watch the soldiers as they entered their vast favela.

Many resisted talking to reporters, fearful of reprisals from drug trafficking gangs.

But one woman, who declined to be identified, told AFP, "I hope things will get better here" following the robust police and military deployment.

The troops include 2,050 paratroopers, 450 sailors and 200 military police.

They are replacing some 1,500 police who had been in place since Sunday. During that time, they have reported 36 confrontations with suspects, leading to 16 deaths and eight people injured and 118 arrests.

In the past week, police have also seized a trove of weapons, including 24 grenades, two machine guns, 100 pistols and rifles, and assorted bullets, as well as more than 1,000 tons of marijuana, cocaine and crack.

Despite aggressive efforts to clean up the favelas ahead of the football extravaganza, violent crime remains a problem in Rio.

The huge slum "pacification" program has been in place since 2008, and aims to shore up security across the city, which will also host the 2016 Olympics.

Police Pacification Units (UPPs) have been installed in 174 Rio favelas, home to around 600,000 people.

In the six years since the pacification program began, murders in districts with a UPP presence have fallen by 65 percent and by 48 percent in Rio as a whole.

However, attacks on police have intensified in recent weeks, suggesting drug gangs are refusing to go quietly.

In early February, a 28-year-old police officer Alda Castilhos was shot dead. A few weeks later, traffickers opened fire on police in Rio's largest favela, Rocinha, leaving two officers injured as they dived to take cover. More incidents were reported in March.

But Rio state's interior minister, Jose Mariano Beltrame, has launched a counter-attack and told AFP in February he "will not shrink" as he cranks up the pacification process.

"We were never under any illusions that the ringleaders who have dominated the favelas for more than 30 years would give up easily," Beltrame said.