A Brazilian senator has accused a minister in President Dilma Rousseff's government of trying to buy his silence in a massive corruption investigation centered on state oil company Petrobras, prosecutors said Tuesday.

The senator, Delcidio Amaral of the ruling Workers' Party, told investigators in statements given as part of a plea bargain that powerful minister Aloizio Mercadante contacted him via an aide to urge him not to testify and offered political and financial support in exchange for silence, according to a newly released document on the plea deal.