Rio de Janeiro (AFP) - An operation by Brazilian military police in Rio de Janeiro on Friday left at least 13 people dead in a number of city center favelas, authorities said.

They were among 14 people who sustained gunshot wounds in the operation close to the Santa Teresa neighborhood, health officials said.

Firefights often break out in favelas during battles between rival gangs or when the police launch operations to combat drug trafficking.

The police said they conducted operations from Friday morning due to "shoot-outs in the area caused by the dispute between rival criminal groups," with local reports indicating that two gangs had been in a turf war since Wednesday.

On Twitter police added that they had "shot 12 criminals" during the operation.

In the Fallet area, security forces were "met by gunfire and there was a battle," the police said.

"After which at least 10 wounded criminals were found in the streets and were taken to the Souza Aguiar hospital," they added.

Authorities said they had seized three assault rifles, 12 pistols and six grenades, pictures of which were posted on the military police's Twitter page.

A video posted on the website of the local O Dia newspaper showed police loading bodies into the back of a vehicle.

A quarter of Rio's population of six million people live in favelas -- informal, poorly-resourced townships populated by low income residents in one of the world's most economically unequal countries.

Insecurity has been on the rise since the city hosted the 2016 Summer Olympic Games. Last year, it registered a record 63,800 murders.

- Insecurity concerns -

As well as rising crime, human rights groups have hit out at the security forces for excessive use of force, particularly in favelas.

In 2017, 1,127 people died during police operations in Rio state, the Public Security Forum NGO said -- a 90 percent increase since 2014.

Also in 2017, 104 security agents were killed, mostly when off duty.

Insecurity is one of the issues that most worries Brazilians in a country that is already one of the most violent in the world.

Story continues

Violence is often blamed on powerful armed gangs such as the Primer Comando de la Capital (Capital First Command) in Sao Paulo and Rio's Comando Vermelho (Red Command).

These groups, many of whose members are in jail, fight for control of the drug trafficking trade.

Occasionally their disputes descend into bloody battles, either in the streets or in the cells.

Far-right President Jair Bolsonaro was swept to victory in elections last year mostly through vowing to get tough on crime.

Last month he issued a decree authorizing gun ownership, while the pro-gun lobby in congress wants to make it legal for citizens to carry weapons for self-defense purposes.

In last October's polls, Wilson Witzel was elected governor of Rio state. Before assuming office he said he would deploy police snipers to shoot suspects even when officers' lives weren't in danger.