Five favelas were targeted by the combined forces in a swoop that started in the small hours, the Rio state security service said in a statement. Their main goal was to stop gangs behind a surge in brazen robberies of commercial trucks.
Brazil's Globo television showed footage of soldiers in camouflage searching residents in the favelas and driving down streets in armored personnel carriers.
Officials said the favelas were Lins, Camarista Meier, Morros de Sao Joao and Engenho Novo in the north and Covanca in the west.
"The armed forces are responsible for the perimeters in some of these regions and based at strategic points," the state security service said. "Some roads are blocked and the airspace is restricted to civilian flights over the sectors where the armed forces are operating."
Rio's airports, however, were not affected.
The big crackdown on Rio's heavily armed criminal gangs came exactly a year after President Michel Temer opened the Olympics.
Rio was the first South American city to host the Games and although the event passed off smoothly, a mixture of corruption scandals, near collapse in the budget and crime has combined into a serious hangover for what should be one of Brazil's richest regions.
