Some 8,500 soldiers and hundreds of police and highway patrol officers have been deployed on to the streets of Brazil's second city to fight organized crime.

The official government gazette reported that President Michel Temer had signed a decree allowing the use of armed forces in Rio. In all, 10,000 troops are to be mobilized.

While they have previously carried out patrols, controlled checkpoints and recovered weapons seized during police raids, the troops are to begin participating in operations against drug traffickers, Defense Minister Raul Jungmann announced at a news conference on Thursday.

Jungmann said there could be consequences from the operation: "It must be taken into account that, given the progress and the point of Rio's criminality, yes, we will have reactions," he said. "It is very important that society understands that it is necessary to face them."

Trucks carrying troops were seen crossing bridges and expressways on Friday in an operation that is to continue until the end of 2018.

A national force policeman on patrol near the Chapadao slums

Out of control

An average of three people have been killed by stray bullets every day in the first six months of the year. Those deaths, plus criminal assaults and shootouts between drug traffickers and police have led to admissions from authorities that much of the city is out of their control.

Adding to the challenge of controlling widespread organized crime, the Brazilian police itself does not have the best reputation for probity.

In a statement on its website, human rights group Amnesty International (AI) said police have continued to use "unnecessary and excessive force, particularly in the context of protests." Amnesty said: "Young people and black men, mainly those living in favelas and other marginalized communities, were disproportionately targeted with violence by law enforcement officials."

Spike in police killings

In a report to the United Nations, which periodically monitors violence in conflict zones and other troubled areas worldwide, Amnesty highlighted the recent spike in killings by Rio police - 182 in the first two months of the year, or 78 percent more than a year earlier.

Jurema Werneck, AI's director in Brazil, said in May, "Brazil has not taken enough steps to tackle the shocking levels of human rights violations across the country, including soaring police homicide rates."

Reporting to the United Nations in May, AI highlighted the recent spike in killings by Rio police: a 78-percent rise to 182 in the first two months of the year.

Some commentators say that placing more troops on the streets of the city may act as an incentive for criminals to try to co-opt or corrupt even more officers.

jm/bk (AFP, Reuters)