Mexican law enforcement authorities are investigating former President Enrique Pena Nieto as part of an inquiry into corruption, the Wall Street Journal (WSJ) reported on Wednesday.

Pena Nieto has become embroiled in the investigation of Emilio Lozoya, the former chief executive of Mexico's state oil firm Petroleos Mexicanos, or Pemex.

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Lozoya is accused of corruption related to a wide-ranging bribery and money-laundering case involving Brazilian construction firm Odebrecht SA. Lozoya, who was arrested in Spain last week, has denied wrongdoing.

"The attorney general's office has evidence that the corruption of Lozoya in Agronitrogenados and Odebrecht reaches to the highest level," a senior law enforcement official told the WSJ.

"The extradition and [any possible] confession of Lozoya are elements that together with ongoing investigations will decide if the former president is charged in the future."

After his arrest in Spain, Lozoya's lawyer Javier Coello Trejo, speaking to a Mexican television station, said his "client didn't act on his own", implying he was following orders by superiors.

The Mexican attorney general's office did not immediately respond to a request for comment.

Odebrecht has been at the centre of one of the world's largest corruption scandals for paying billions of dollars in bribes across the region in exchange for public-works contracts.

Previous investigations have touched nearly every country in Latin America, with presidents impeached and officials arrested.

Corruption scandals

Pena Nieto, who completed a six-year term in 2018, could not immediately be reached for comment. He has previously denied receiving bribes from Odebrecht.

During his mandate, the former president became entangled in numerous corruption scandals, among those was the disappearance of 43 students, spyware software purchased by the government to monitor journalists and human rights lawyers, and early in his administration the purchase by his wife of a mansion with financing from a builder who previously received state government contracts while Pena Nieto was governor.

Former First Lady Angelica Rivera said she had money to buy the house from her career as a soap opera star, but returned it to avoid any controversy.

President Andres Manuel Lopez Obrador said he does not want to pursue former presidents in court, though he has suggested the possibility of holding a referendum on whether former presidents should face trial.

Lozoya's detention was a major success for Lopez Obrador, a leftist who won power on an anti-fraud platform and who has sought to paint former administration officials as members of a corrupt elite since taking office in December 2018.