Brazil's attorney general's office says it will seek $1.55 billion from six construction and engineering companies for their alleged involvement in a massive kickback scheme at state-run oil firm Petrobras.

The amount includes $111 million in compensation for public money that prosecutors say was stolen from Petrobras, plus $333 million in fines and $1.11 billion in punitive damages.

The action Friday is the latest aggressive step by prosecutors who say they've uncovered the biggest yet known corruption scheme in Brazil.

Prosecutors allege top construction and engineering firms paid bribes for more than a decade to Petrobras executives in exchange for winning inflated contracts with the oil firm.

The firms named in Friday's action include: Camargo Correa; Sanko; Mendes Junior; OAS; Galvao Engenharia; and Engevix.