The attacks took place on Monday to the west of the Brazilian city, where opposing criminal gangs fight for territorial control.

Military police said it arrested 12 suspects involved in the fires, and prevented 15 people from setting a cargo truck ablaze in one of the city's main gateways.

Industry group Rio Onibus said 20 of the vehicles set alight were city buses, five were part of the city's rapid transit fleet and the rest were chartered or tourism buses.

The blazes came after police killed the nephew of the leader of the state's largest militia during the operation, according to authorities, which the city's state governor Claudio Castro said was a "heavy blow" to them.

The dead man has been named by local media as Matheus da Silva Rezende.

Rio's militias operate in the region and are often composed of current and former police officers.

Originally established to serve poor areas ravaged by drug gangs, the militias morphed into criminal units operating in multiple different rackets.

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Describing the crime chief who was killed, Mr Castro said: "In addition to being related to the criminal [head of the militia], he acted as the paramilitary group's 'man of war', being the main person responsible for the turf wars that terrorise residents in Rio."

The fires disrupted the city's transport system, while classes were cancelled in schools in the area.