Rio de Janeiro's police have killed more than 1,500 people in the last five years, driving up the Olympic host's already high violent death rate, Amnesty International said Monday.
A report by the human rights group accuses Rio police of disproportional use of lethal force and of what appear to be extrajudicial executions.
"At least 16 percent of the total homicides registered in the city in the last five years took place at the hands of on-duty police –- 1,519 in total," Amnesty said.
The report -- "You killed my son: Killings by military police in Rio de Janeiro" -- alleges police have a "shoot first, ask questions later" policy and act with near impunity.
It comes as security officials prepare to cope with the Olympics in a year from this week, when tens of thousands of people will attend the world's biggest sporting event.
Officials say they will deploy some 85,000 police and soldiers, most of them focusing on a relatively small zone where the Olympic sites, hotels and beaches are located.
Brazil is one of the most violent of the world's countries that are not at war. More than 50,000 people were murdered in 2012, according to the most recent UN figures.
Crime in Rio has gone down slightly over the last year, official statistics show, in part because of intensive policing in slum areas known as favelas.
However, the city still sees more than three people murdered every day and there are frequent armed clashes between paramilitary police and drug gangs in favelas.
Even parts of the supposedly safe city center are plagued by muggers.
Amnesty said that investigating the details of fatal shootings by police is difficult. However in the Acari favela, at least nine out of 10 killings by police in 2014 "strongly suggests the occurence of extrajudicial executions."
"Rio de Janeiro is a tale of two cities: on the one hand, the glitz and glamor ... on the other, a city marked by repressive police interventions that are decimating a significant part of a generation of young black and poor men," said Atila Roque, director at Amnesty International Brazil.
"Brazil's failed war on drug strategy to tackle the country’s very real public security crisis is backfiring miserably."
The human rights group accused police of systematic cover-ups.
"Such killings are hardly investigated," Amnesty said.
"In practice, many cases are filed as 'resistance followed by death,' which prevents independent investigations and shields the perpetrators from the civilian courts."
In many cases police tamper with the evidence, moving bodies or placing weapons next to them, in order to escape further investigation, the report said.
Police were not immediately available for comment on the report.