RIO DE JANEIRO, April 8 -- When police killed a drug kingpin in a Rio de Janeiro favela last month, armed men quickly surrounded a bus, forced the passengers to disembark and set it on fire in the middle of an avenue.

"They boarded, told me to get the passengers off, and set it ablaze. It happened very fast," 48-year-old driver Marcio Souza told AFP, still shaken by the ordeal.

"It was a horrible feeling that I wouldn't wish on anyone."

Scenes like this are common in the city of nearly seven million people, which is one of the most visited tourist destinations in the world.

Clashes are frequent between police and armed criminal groups that dominate Rio de Janeiro's sprawling favelas.

To retaliate, criminals often seize buses in a sho...