Brazil has stepped up its efforts to shore up security during the upcoming football World Cup as the country's armed forces moved into Rio de Janeiro's most violent slums to crack down on drug gangs.

More than 2,000 troops, 450 marines and 200 police officers entered the Mare slum complex early on Saturday without firing a shot, and were planning to remain there until July 31, a little more than two weeks after the end of the games.

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.

"We are monitoring the area closely and patrolling will be constant," Major Alberto Horito said. 

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 news agency: "I hope things will get better here" after the robust police and military deployment.

Years of limited success

The move follows a wave of attacks on police posts in slums that had previously been occupied under Rio's "pacification" programme launched in 2008.

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

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.

However, attacks on police have intensified in recent weeks, suggesting drug gangs are refusing to go quietly and prompting President Dilma Rousseff to sign off on the use of the armed forces to occupy the slum.

Agencies