Updated

Rio de Janeiro's police force operates with "total impunity," targeting mostly young, mostly black and mostly poor people in the Olympic city's violent slums for extrajudicial executions, Amnesty International alleged in a report Monday.

The group accuses Rio's police of wielding an "unnecessary and disproportional use of force" and suggests racism has helped institutionalize police killings in the city.

It also says police often try to cover up executions by labeling them "resistance killings" in which victims allegedly die in a gunbattle with officers or by planting weapons on corpses.

The report also criticizes police oversight bodies and the public prosecutor's office, saying they largely fail to investigate such killings.

"The police continue to regularly use force in an arbitrary, unnecessary and excessive manner, with total impunity," the report's executive summary said.

The report was based on an investigation into 10 police killings in 2014 and 2015 in the Rio slum of Acari, which found that four of the victims were wounded or had surrendered before they were killed, four were fired on without warning and another was fleeing when he was gunned down.

Rio's state security secretariat declined to comment directly on the report, saying in a statement they hadn't seen the study's methodology. But the statement added that since 2009, officers have been rewarded for cutting down on lethality, including "resistance killings." It also stressed that in June, homicides in Rio state dropped to their lowest levels in 24 years.

Brazil has more homicides than any other country, with some 56,000 people slain in 2012.

Amnesty's report included five recommendations to the state government, which included a call to guarantee independent investigations into all police slayings.