Updated

Brazilian police carried out a "significant proportion" of the 48,000 murders that swept Brazil last year, according to a U.N. report released Monday, casting doubt on the government's ability to curtail drug violence and reign in vigilante militias.

The report by U.N. special envoy on extra-judicial killings Philip Alston said police murder three people a day on average in Rio de Janeiro, making them responsible for one in five killings in the city, which is plagued by drug-gang violence and roving militias of off-duty police.

Rio de Janeiro State Security Chief Jose Beltrame dismissed the findings, saying Alston spent less than two weeks in Brazil and did not fully understand what was happening.

"He is a person who comes from Australia ... (and) came up with a shortsighted report of police operations," Beltrame said. "I want him to prove it."

The U.N. report found that police are rarely punished for their involvement and many Brazilians are resigned to the violence, seeing no other way to fight the drug gangs that rule the slums.

Alston toured some of Brazil's most crime-ridden areas in November, gathering statistics from the government, police and NGOs, and interviewing local commanders, top ministers, activists and more than forty witnesses to police abuses. He presented his findings to the U.N. Human Rights Council in Geneva on Monday.

Clashes with police killed a record 1,260 civilians in Rio de Janeiro state last year — nearly the same number of all people murdered in New York, Chicago and Los Angeles combined in 2007. The Brazilian tally was in fact likely higher: a third of precincts lacked computers to report any murders.

Most police killings occurred during "acts of resistance" — police jargon for armed confrontations with civilians, Brazil's Institute of Public Safety said in a January report.

Alston said the deaths were "politically driven" because they were "popular among those who want rapid results and shows of force."

"A remarkable number of police lead double lives," Alston told reporters Monday. "While on duty, they fight the drug gangs, but on their days off, they work as foot soldiers of organized crime."

Off-duty police militias are relatively new in Rio de Janeiro, moving into shantytowns and charging residents monthly fees to protect them from drug gangs. Federal and state officials estimate that militias now control at least 15 percent of Rio's more than 600 slums.

"For residents, life under the control of a militia is often just as violent and insecure as life under the control of a drug gang," the report concluded.

The report focused on one operation that involved 1,350 police and led to the deaths of 19 people in Rio de Janeiro's Alemao shantytown in June 2007. Independent experts determined that several victims had likely been executed, the report said.

Alston accused police of using such large-scale operations for political reasons.

"Local officials claim that these impressive sounding 'mega-operations' are protecting residents from drug gangs, but the operations have hurt ordinary people far more," he said. "This is policing by public relations stunt."