(Adds response from Grana)
LIMA, Nov 13 (Reuters) - The Peruvian attorney general's office is investigating construction group Grana y Montero for alleged involvement in bribes paid to a former president by its Brazilian partner Odebrecht, a lead prosecutor said.
Speaking in a televised interview with America Television, Hamilton Castro said that his office has been investigating Grana and other local partners of scandal-plagued Odebrecht despite not speaking publicly about it previously.
"There is an investigation against the partner companies ... against Grana y Montero and others," Castro, the lead prosecutor on the Odebrecht case, said in the interview late on Sunday.
Grana said on Monday that it had not been notified that the company or any of its directors, executives or collaborators were included in the Odebrecht probe.
"Notwithstanding ... we wish to record our deep interest in knowing the truth and our willingness to collaborate fully in the investigations," Grana said in a statement.
Opposition lawmakers have accused prosecutors of political bias for not targeting Grana, Odebrecht's most important partner in Peru. Attorney General Pablo Sanchez has dismissed the allegation as retaliation for a separate probe into campaign financing.
Grana's shares on the Lima and New York stock exchanges, which have plummeted since the Odebrecht scandal broke nearly a year ago, closed more than 4 percent lower on Monday.
The company has repeatedly denied any wrongdoing and said an internal probe turned up no evidence that its employees knew about or took part in bribes that Odebrecht has admitted paying to local officials in exchange for lucrative contracts.
Castro said an Odebrecht executive who turned state's witness, Jorge Barata, told prosecutors the companies that Odebrecht partnered with on two highway projects had paid their share of bribes given to former Peruvian President Alejandro Toledo, who denies wrongdoing.
"That statement must be corroborated," said Castro, who did not provide additional details on the investigation into Grana.
Last week Peru's Congress passed legislation to expand a raft of new anti-graft rules and financial restrictions to Grana and other local partners of Odebrecht - driving a more than 20 percent drop in its share value on Friday.
Reporting by Mitra Taj; editing by Susan Thomas and Rosalba O'Brien