Critics of the Brazilian Military Police have charged officers are provoking violence among largely peaceful protesters. In Monday's protest at least one man was injured by a rubber bullet fired at close range, the BBC said.
Other protesters say police make no effort to distinguish between the relatively small number of protesters vandalizing property and the vast majority who are not.
Amnesty International Brazil Director Atila Roque said he's seen police "overuse" tear gas and fire rubber bullets indiscriminately into crowds to disperse protesters.
"We saw police chasing people, trapping them in the streets, in a bar, even a hospital, and then attacking them with tear gas," he said.
Rio police trainers said officers are being taught to use force proportionately and have met with law enforcement trainers from the United States and other countries to learn proper crowd control tactics.
"Our riot police are well trained, they have the proper techniques and equipment," said Juliana Barroso, who is in charge of police training in Brazil. "What may be missing is reflecting on where the limits are. When I am out there, when do I keep going and when should I stop?"
The nation has been rocked by protests that were sparked over an increase in municipal transportation fees but quickly ballooned into general protests over poor public services and what's seen as widespread government corruption in Brazil.