MEXICO CITY (Reuters) - Mexico’s government said on Thursday it would investigate funding of critical coverage of President Andres Manuel Lopez Obrador during his 2018 election bid on suspicion it received illicit support from his adversaries.

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Santiago Nieto, head of the finance ministry’s financial intelligence unit, said the government would investigate funding of the series “Populismo en America” (Populism in America) that featured an episode dedicated to Lopez Obrador.

Nieto said the documentary was part of a “dirty campaign” aimed at discrediting Lopez Obrador during the election.

Standing beside Lopez Obrador at his regular morning news conference, Nieto said the documentary got funding from a group whose backers included construction firm OHL Mexico, now known as Aleatica, and the government of the State of Mexico.

Aleatica “has no direct or indirect relation with the ‘dirty campaigns’ nor has it directly or indirectly financed any positive or negative communication efforts,” it said in a statement.

An investigation would determine whether the funding contravened Mexico’s campaign finance laws, Nieto said.

The company said it would cooperate with the investigation.

OHL Mexico changed its name to Aleatica last year after being sold to IFM Investors.

The State of Mexico is run by the Institutional Revolutionary Party (PRI), the party of former President Enrique Pena Nieto, who was state governor before he took the top job.

OHL Mexico was a successful contractor under Pena Nieto during his tenure in the state between 2005 and 2011.

The investigation may raise questions about the leftist Lopez Obrador’s repeated statements that he would not pursue his political adversaries once in office, a position that has not always gone down well with his core supporters.

Lopez Obrador mentioned the documentary in April 2018 during a video address to supporters, in which he accused his political adversaries of waging a “dirty war” against him.