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By Associated Press

A local Mexican news outlet alleges that Mexican President Enrique Peña Nieto heavily plagiarized his thesis for his law degree.

Aristegui Noticias on Sunday published an online report based on an analysis of the embattled president's thesis by a group of academics, which it said was then corroborated by the news outlet.

It said 29 percent of the thesis was material lifted from other works, including 20 paragraphs copied word-for-word from a book written by former President Miguel de la Madrid without citation or mention in the bibliography.

Mexican President Enrique Peña Nieto delivers a speech next to the U.S. Vice President Joe Biden (not pictured),at Los Pinos presidential residence in Mexico City, Mexico February 25, 2016.HENRY ROMERO / Reuters

A spokesman for Peña Nieto responded Sunday that the president had completed all requirements for his law degree and downplayed the relevance of "style errors" in academic work done 25 years earlier.

Peña Nieto did not mention the controversy on Monday as he spoke in front of students at his old elementary school in Toluca to inaugurate the first day of the new school year Monday,.

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The thesis titled "Mexican Presidentialism and Alvaro Obregon" was submitted in 1991 to the Panamerican University.

The news website is run by journalist Carmen Aristegui, who in 2014 reported that Peña Nieto's wife was purchasing a house with financing from a government contractor. The first lady eventually gave up the house and in recent months Peña Nieto has said he understands why the so-called "White House" scandal upset so many Mexicans.

Several months after that investigation was published Aristegui was fired by the radio station where her investigative team worked. They have since re-emerged online.

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A poll by the national newspaper Reforma this month found Peña Nieto's approval rating at 23 percent, the lowest rating for any president since it began the survey in 1995. The margin of error was 3.3 percentage points.

It's not the first time that Peña Nieto's academic rigor has been called into question.

When he was a candidate for the presidency in 2011, Peña Nieto stumbled when asked to name three books that influenced him. He managed the Bible, before fumbling through other mismatched authors and titles.

Recent charges of plagiarism have not been limited to Mexico.

RELATED: Mexico's Enrique Peña Nieto Increasingly Unpopular: Pew Survey

In 2006, a scholar at the Brookings Institution found that now-Russian President Vladimir Putin in earning his graduate degree had copied pages of material from a book written by two American professors.

In 2012, Hungary's President Pal Schmitt - whose role was largely ceremonial - resigned after a scandal over his doctoral dissertation.

Earlier this year, a German university decided to let the country's defense minister, Ursula von der Leyen, keep her doctorate after plagiarized passages were found in her dissertation.

Last month, potential first lady Melania Trump gave a speech at the Republican National Convention using phrases nearly identical to those in an earlier speech by Michelle Obama.

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