(Adds comment from Skanska Brasil)
BRASILIA, March 18 (Reuters) - Brazil's Comptroller-General Office on Wednesday added another six construction and engineering firms to an investigation of contractors that allegedly participated in a corruption ring at state-run oil company Petrobras.
Newly included in the case were Tome Engenharia, Egesa Engenharia, Carioca Christian Nielsen, Skanska Brasil, Eit Empresa Industrial Técnica and MPE Montagens e Projetos Especiais, the agency known as CGU said in a statement.
A total of 24 of Brazil's top builders are being investigated for suspected overpricing of contracts in a multibillion-dollar scheme that funneled bribes to Petrobras executives and politicians.
The case may exclude the companies from new contracts with Petroleo Brasileiro SA, as the oil company is formally called, and lead to fines and other penalties.
Brazil's biggest-ever corruption scandal is rippling through various sectors of Brazil's economy. Large infrastructure projects will likely be stalled with so many engineering firms under investigation.
The investigation has so far led to 20 indictments of 103 people on racketeering, bribery and money laundering charges, including three former Petrobras senior managers and executives from Brazil's leading construction and engineering firms.
The CGU began investigating eight construction companies directly implicated in the case in December, leaving many of them in financial trouble as they lost revenue and access to capital markets.
Last week, Alumini Engenharia, GDK SA, Promon Engenharia, Andrade Gutierrez SA, Fidens Engenharia, Sanko-Sider, Odebrecht SA, Odebrecht Óleo e Gás , Odebrecht Ambiental and SOG Óleo e Gás were included in the CGU investigation.
The companies denied any wrongdoing. Odebrecht, Brazil's largest diversified engineering firm, last week said it never took part in any cartel and that it won all its contracts with Petrobras in accordance with the legislation.
Skanska Brasil, a subsidiary of Sweden-based Skanska AB , said it ran its business with a high level of integrity and was at the disposal of authorities to collaborate in the investigation.
The Petrobras scandal has fueled protests against the government and calls for the impeachment of President Dilma Rousseff, whose popularity has plummeted. (Reporting by Anthony Boadle; Editing by Guillermo Parra-Bernal and W Simon; Editing by Ken Wills)