Soldiers in camouflage helmets and black boots edged forward, guns poised. Every doorway and corner of this cobblestoned back street is treated as a threat.

Around them, everyday life continued. Mothers washed bath mats. Teenagers played cards. A man with a loudspeaker sold shrimp from his Kombi van. Only a 5-year-old boy sitting on the curb looked up inquisitively from his plate of biscuits.

Maré — one of the most dangerous of Rio de Janeiro’s slums, called favelas — has grown used to poverty, mob law, indiscriminate incursions by deadly police units and now — military occupation by thousands of federal troops.

A collection of 16 enclaves straddling two strategic roads leading to Rio’s international airport, Maré was a war zone between rival drug gangs for roughly three decades. Now it’s a key battleground in the authorities’ effort to “pacify” the city’s favelas ahead of the 2014 World Cup, which begins June 12.

Thirty-seven pacifying police units (UPPs) have been installed in favelas since 2008 to wrest control from the gangs. But a recent upsurge in violence against police in pacified favelas has caused a crisis.

The situation in Maré was so volatile that 2,700 troops have been deployed to keep the peace until July 31, two weeks after the tournament ends.

“We are not thinking about the World Cup. We are thinking about Rio’s citizens. We are thinking of the police who are dying,” Rio Security Secretary José Mariano Beltrame told reporters after the announcement.

But many residents doubt the sincerity of that promise and fear the consequences if it proves hollow.