Senator Delcidio Amaral, who leads President Dilma Rousseff's Workers' Party in the upper house, was the first sitting legislator to be arrested in the widening corruption scandal.
"He is in preliminary detention. He was detained in Brasilia and has already arrived at the police station," a press officer for the attorney general's office told AFP.
Police in Rio de Janeiro also arrested BTG Pactual investment bank CEO Andre Esteves, who is estimated by Forbes magazine to have personal wealth of some USD 2.2 billion, overseeing about USD 200 billion in assets. Search warrants were issued for residences and offices in Brasilia, Sao Paulo, Rio and Mato Grosso.
According to prosecutors, Amaral was recorded suggesting to the son of the imprisoned former head of Petrobras' international division, Nestor Cervero, that he should not cooperate with authorities.
Amaral even told the son that he could help Cervero flee Spain with payments of about USD 13,500 a month for his family, a spokesman at the Supreme Court told AFP. Cervero has agreed to cooperate with prosecutors in hopes of being given a lighter sentence, which could be as much as five years.