Two top Brazilian businessmen have been arrested as part of a major investigation into corruption at state-owned oil giant Petrobras.
Marcelo Odebrecht heads the Odebrecht group - Latin America's largest construction conglomerate.
Also detained is Otavio Azevedo, boss of Andrade Gutierrez, another top construction company.
Investigators allege firms paid corrupt officials in order to get lucrative Petrobras contracts.
The scandal has rocked Brazil's governing Workers' Party, with top politicians accused of taking bribes.
But President Dilma Rousseff, who chaired Petrobras when much of the corruption is believed to have taken place, has been cleared of involvement.
Analysis: Daniel Gallas, BBC South America Business Correspondent
Odebrecht is one of Brazil's most successful construction firms - with a huge presence in countries like Angola and Mozambique.
Among its many works is the Sao Paulo stadium used in the opening of last year's Fifa World Cup.
Just last month its president took pride in the fact that his company had not been implicated in the wide-ranging investigations into Petrobras.
But today Marcelo Odebrecht is under police custody.
Even before the Petrobras scandal, Odebrecht was accused by critics of benefiting from close relations with the Brazilian government.
The accusation led Brazil's investment bank BNDES to reveal details of how much money it lent to Odebrecht to build infrastructure projects in Cuba and Angola.
Now Odebrecht is at the centre of Brazil's costliest corruption scandal.
Odebrecht had been named by former Petrobras executives as one of the companies that allegedly paid bribes in exchange for contracts with the oil firm, but until now the firm had not been targeted by investigators.
Odebrecht said in a statement (in Portuguese) its offices had been raided, and arrests had been made, but called them "unnecessary" as it had been co-operating with the authorities.
Andrade Gutierrez also said it was co-operating, according to the Reuters news agency, but had no connection to the investigation into Petrobras.
Announcing the arrests, a police spokesman said the operation sent a "clear message" no one would escape their attention, no matter how big they were.
Petrobras' investments alone represent 2% of Brazil's gross national product, and its downturn has harmed a national economy struggling as a result of low commodity prices.
The corruption scandal has cost Petrobras over $16bn (£10bn), including $2bn (£1.2bn) that went straight to corrupt executives and firms.