A Federal investigation targeted Luiz Carlos Velloso, a former Undersecretary of Transportation for the State Government, and Heitor Lopes de Souza, a director for subway operator Riotrilhos.

Both individuals will be charged with money laundering and taking bribes tied to contract extensions for the subway line.

The extension of metro linha four westwards towards the main Olympic cluster of Barra de Tijuca is billed as one of the main legacy incentives of Rio 2016.

It is now used by thousands of Brazilians to speed-up journey times between the suburbs and the city centre.

The project was dogged by a succession delays in the build-up to the Games and was only accessible for ticket-holders and accredited personnel during the Games last August.

The line four extension is thought to have cost around R$10 billion (£2.6 billion/$3.2 billion/€3 million).

Police now believe that many of the delays and cost increases related to fraudulent fees paid by construction companies.

The project was carried out by the Rio Barra Consortium: a body made up of three major contractors, Carioca Engenharia, Odebrecht and Queiroz Galvão.

This forms part of the ongoing "Operation Car Wash" investigation which has ensnared dozens of leading Brazilian politicians and businessmen.

Rio 2016 has not escaped the probe.

Odebrecht are among five companies under investigation who were also involved in constructing Olympic venues.

The others are OAS SA [OAS.UL], Andrade Gutierrez SA, Queiroz Galvao SA and Carioca Christiani Nielsen Engenharia SA.

Former Rio State Governor Sérgio Cabral has also denied wrongdoing after being arrested late last year and accused of embezzling $65 million (£52 million/€61 million) due to be spent on construction projects, including ones connected to Rio 2016.

Cabral, Governor from 2007 until 2014, is accused of taking a five per cent cut on every contract negotiated to construct buildings in Rio de Janeiro.