MEXICO CITY (Reuters) - Emilio Lozoya, the former head of Mexican oil firm Pemex, on Thursday denied he was involved in shifting cash to President Enrique Pena Nieto’s campaign, saying bank accounts where millions of dollars were allegedly deposited were not his.

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In a nearly hour-long news conference after appearing at the attorney general’s office in Mexico City, Pena Nieto ally Lozoya rejected claims published by Brazil’s O Globo newspaper that he had taken $10 million in bribes in 2012 from a former executive at Odebrecht SA, Latin America’s biggest construction firm, in return for a refinery contract.

Odebrecht is involved in a sprawling corruption saga in which has already paid $3.5 billion in settlements in the United States, Brazil and Switzerland, embroiling politicians across Latin America.

Citing bank documents, a separate report by civil society group Mexicans Against Corruption said payments had been made when Lozoya was a senior official in the campaign that clinched the presidency for Pena Nieto 2012.

Lozoya has already taken to Twitter to deny the reports, which are a major blow for the already unpopular Pena Nieto, less than a year before a tight election in which his party faces an uphill battle to retain the presidency.

On Thursday Lozoya specifically rejected accusations that any of the money he is alleged to have received ended up in the campaign’s coffers, and denied holding the bank accounts where the bribes were supposedly paid.

“I categorically deny any participation in these accusations and as such, I have no comment to make over any possible illegal campaign financing in 2012. Therefore, I conclude that accusation is false,” he said.

This week, the president’s office denied any Odebrecht cash was funneled into the campaign, calling the accusations “absurd, irresponsible and in bad faith”.

Lozoya told reporters on Thursday he only knew one of the three Odebrecht executives - Luis Alberto de Meneses Weyll - who have allegedly testified against him, according to press reports, and that was before he took the helm at Pemex.

“I don’t know the other two, nor have I had any contact with them,” he said.

Mexico’s attorney general’s office, which has faced criticism for its seeming reluctance to investigate high-profile Mexicans involved in the scandal, said on Thursday it expected to receive more information on the case from Brazilian prosecutors in the coming days.

Odebrecht has admitted to U.S. and Brazilian prosecutors that it paid $10.5 million in bribes in Mexico, but details have not been made public.

Corruption scandals have hounded 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.