Campaign group Amnesty International says Brazil’s military police have been responsible for more than 1,500 deaths in the city of Rio de Janeiro in the last five years.
Amnesty says it has found evidence that police killings were often illegal, with officers shooting suspects who had surrendered or had been wounded.
There has been no response so far from Brazil’s military police.
Police unions earlier said the number of officers killed was also very high.
In Rio de Janeiro alone, 114 police were killed in 2014, according to the civilian police union Sindpol.
Police officers have in the past denied being “trigger happy”, saying they act in self defence when they come under fire from drug dealers in Rio’s sprawling favelas.
In a report published a year before Rio is due to host the 2016 Olympic Games, Amnesty said police were decimating a significant part of a generation of poor, young, black men.
According to statistics released by Amnesty, nearly 16% of the total homicides registered in the city in the last five years took place at the hands of on-duty police officers.
In 2012 more than 50% of homicide victims were aged between 15 and 29, and 77% of them were black, the figures suggest.
Amnesty also said that incidents of police killings were rarely investigated and those responsible did not often face justice.
But the prosecutor’s office in Rio de Janeiro state told BBC Brasil that 587 police officers were accused and brought to justice between 2010 and 2015.
Atila Roque, director at Amnesty International Brazil, said the country’s strategy to tackle its drugs and violence problem was “backfiring miserably and leaving behind a trail of suffering and devastation”.
The pressure group says military police across Rio de Janeiro have regularly used unnecessary and excessive force during security operations in the city’s poor neighbourhoods.
‘Fighting for justice’
Maria de Fatima Silva’s son was killed in a police raid in Rio’s Pavao-Pavaozinho favela in April 2014.
The case of Douglas Rafael da Silva Pereira, a professional dancer, triggered clashes between the police and residents outraged by his death.
It is still being investigated but Ms Silva fears his case will eventually get shelved, so she has started her own private investigation.
She told BBC Brasil’s Luis Kawaguti that witnesses were afraid to testify after allegedly being threatened.
She said support from campaign groups had given her the courage to fight for justice for her son.