Human Rights Watch says police officers in the Brazilian cities of Rio de Janeiro and Sao Paulo have killed more than 11,000 people in the past six years, many of them execution-style.
The rights group said in a new report Tuesday that few of the officers have been charged in the extrajudicial killings, which are often labeled in police reports as the deaths of suspects who resisted arrest.
The group said it obtained credible evidence in 51 "resistance" cases that contradicted officers' claims that victims died in a shootout.
Human Rights Watch also said that police often cover up their killings by destroying crime scene evidence. The group said its examination of the 51 cases indicated a much broader problem.
There was no immediate comment from the Rio or Sao Paulo police.
Human Rights Watch is recommending the creation of specialized units within state prosecutors' offices to investigate the so-called "resistance" killings and ensure that officers responsible for extrajudicial executions are brought to justice.
Brazil will host the World Cup football (soccer) tournament in 2014 and the Summer Olympic Games in 2016. Brazil is South America's biggest economy.
Some information for this report was provided by AP, AFP and Reuters.