A close former aide of Mexican President Enrique Pena Nieto, "categorically denied" allegations he received $10 million in bribes from Odebrecht, the Brazilian builder which has business interests in the energy sector, during the 2012 presidential campaign and later when he headed state oil company Pemex.
Brazil's O Globo newspaper reported on documents alleging that Pena Nieto's confidant Emilio Lozoya received bribes from a former Odebrecht executive from 2012 to 2016 in return for a contract at Mexico's Tula refinery.
Citing bank documents, a further report by civil society group Mexicans Against Corruption said payments had been made when Lozoya was a senior official in Pena Nieto's campaign.
The allegations linked Lozoya to the $10.5 million in bribes scandal-plagued Odebrecht has admitted to paying in Mexico.
Corruption scandals have dogged Pena Nieto's government, playing into the hands of leftist opposition candidate Andres Manuel Lopez Obrador, who is preparing a third run for office next year on an anti-graft ticket.
Among Lopez Obrador's policy proposals is a close revision of energy contracts signed under Pena Nieto, who opened up Mexico's oil industry to private investment, a structural overhaul seen as perhaps the president's biggest achievement.
Lozoya, who resigned as Pemex chief in 2016, posted on Twitter on Aug. 13 that he had never participated in corrupt practices, calling the allegations "absolutely false."
"Supposing there were accusations against me by confessed criminals, it is important to mention at least that these people can say anything in exchange for a reduced sentence," he wrote in a letter appearing on his Twitter account.
Asked for comment, the Mexican president's office referred to a statement by the attorney general's office, which on Aug. 13 said it had not yet received full information about the case from Brazilian prosecutors. Odebrecht did not immediately respond to a request for comment.
The Mexican prosecutors said they had interviewed nine former Pemex officials along with 10 other officials linked to three Odebrecht contracts.
The statement said Mexico had not accepted a settlement offer by Odebrecht, and would not accept any deal based on limiting punishment to those found to be involved.
Since settling in the U.S., Brazil and Switzerland for a record $3.5 billion, Odebrecht has sought to negotiate leniency deals that would allow it to keep operating in other countries across Latin America.
Odebrecht admitted in the settlement with U.S. and Brazilian prosecutors to paying bribes across 12 countries to win contracts, including in Mexico.