RIO DE JANEIRO/SAO PAULO (Reuters) - Brazilian federal police said they had raided the offices of six highway operators on Wednesday, taking multiple executives into custody, the latest development in a wide-ranging corruption crackdown in South America’s largest country.

Police detained 19 people and executed various search and seizure warrants throughout southern and southeastern Brazil, according to a law enforcement statement.

Authorities are investigating an alleged corruption ring in which public officials in the southern state of Parana received about 35 million reais ($8.67 million) in bribes between 1999 and 2015 from companies awarded highway contracts, the statement said.

The police said the operation was the 55th phase of Brazil’s so-called Car Wash investigation, which started in 2014 and has deeply shaken Brazil’s business and political establishment. Corruption has become a major campaign theme heading into October presidential and congressional elections.

Highway operator CCR SA said in a securities filing that police raided the firm’s headquarters, the offices of subsidiary RodoNorte, and the residences of current and former executives. The police also took Jose Alberto do Rego Moita and Claudio Jose Machado Soares, the chief operating officer and former chief executive of RodoNorte, respectively, into five-day temporary custody, the firm said.

CCR said that it was working to clarify the facts and that an internal investigative committee would present its findings to the board, which would take any required measures.

Ecorodovias Infraestrutura e Logistica SA said in a separate filing that three of its offices in Parana and Sao Paulo were raided, and Evandro Couto Vianna and Mario Cezar Xavier Silva, both executives at subsidiaries, were taken into temporary custody.

Ecorodovias said it was cooperating with the authorities and had provided all requested information.

TPI Triunfo Participações e Investimentos SA said in its own filing that it had cooperated with a police raid on its headquarters and that of its subsidiary Econorte. Triunfo Chairman Luiz Fernando Wolff de Carvalho had been detained and resigned from his post, it said.

A privately-operated firm, Caminhos do Parana, said in a statement sent to Reuters that it was also a target of the operation, and that its chief executive was among those arrested.

“The company regrets what has occurred and considers jail unnecessary, given that the firm has been giving (the police) the necessary clarifications and has never declined to cooperate,” Caminhos do Parana said.

While state-run oil firm Petroleo Brasileiro SA, known as Petrobras, has been the most heavily affected by the Car Wash probe, the infrastructure sector has also been the target of investigations.

Brazil-listed shares in CCR were down 5 percent in early afternoon trade, while Ecorodovias fell 2.8 percent and Triunfo fell 2.3 percent. Brazil’s benchmark Bovespa index was up 0.3 percent.