ZURICH (Mar 18): Switzerland's attorney general said on Wednesday he has uncovered over 300 accounts at more than 30 Swiss banks that he believes are linked to money laundering and corruption at Brazil's state-run oil firm Petroleo Brasileiro SA.

The scandal, involving billions of dollars of allegedly misappropriated funds, has reached the highest levels of power in Brazil, where about 1 million demonstrators turned out over the weekend to vent their anger and call for the impeachment of President Dilma Rousseff, who was chairwoman of Petrobras' board when much of the alleged graft occurred.

Investigators in the alpine nation said they are looking into eight Brazilians in connection with their probe, as well as other, as yet unidentified people after it found evidence that senior executives at Petrobras and suppliers used accounts at more than 30 Swiss banks to launder money.

Switzerland has frozen roughly $400 million in Swiss accounts, but said on Wednesday it will return $120 million to Brazilian officials after a working visit to the country.

"The release of over $120 million reflects Switzerland's clear intention to take a stand against the misuse of its financial centre for criminal purposes and to return funds of criminal origin to their rightful owners," Switzerland's attorney general said in a statement on Wednesday.

Rousseff has denied knowledge of corruption at Petrobras and has urged a thorough investigation.

Brazilian prosecutors said on Monday they had secured commitments to return 500 million reais ($154 million) of money funnelled off Petrobras contracts to public coffers through plea bargain deals. They said 182 million reais ($56 million) had been received so far.