Former Senator Delcídio do Amaral described as "surreal" the notion that former President Luiz Inácio Lula da Silva was not aware of a giant corruption scheme active during his tenure, in testimony on Monday marking the start of the trial against the man that ran Brazil from 2003 to 2010.

On trial for accepting bribes and money laundering in connection to a beachfront apartment, Lula says he has done nothing wrong, denies ownership of the property and denounces his prosecution as a witch-hunt. He has appealed to the United Nations saying his human rights have been violated by the investigation.

The trial is part of a broad probe into a massive government corruption scheme centered on the state-run oil company Petrobras in which the excess from overpriced contracts was used to pay political bribes.

"The president did not get involved with the details, but he was absolutely aware of the interests that encircled the management at Petrobras," Amaral said in testimony that was released as recorded video.

"And then he (Lula) says 'I didn't know'," Amaral added. "But the whole political class and all the Flamengo football fans knew. So it's surreal that kind of affirmation."

Amaral was from the ruling Workers Party and was a key ally of Lula and former President Dilma Rousseff in the Senate until he was arrested last year for corruption and turned state witness in return for a lesser sentence.

In a statement, Lula's lawyers said no testimony given on Monday contained any proof that the former president had committed any crimes in relation to the Petrobras scandal or that he owned the beachfront apartment.