MEXICO CITY - Thousands of people marched through Mexico City on Sunday to denounce the July 1 election of Enrique Pena Nieto as president, though the protest was smaller than one held earlier this month.

Pena Nieto's capture of the presidency for the Institutional Revolutionary Party, or PRI, has been challenged by his rival, leftist runner-up Andres Manuel Lopez Obrador, who alleges the PRI resorted to vote-buying and money laundering to win.

Lopez Obrador is seeking to invalidate the PRI victory at the federal electoral tribunal, and the former mayor of Mexico City has pledged to keep the pressure up on Pena Nieto with rallies around the country starting at the end of this month.

On Sunday, student groups dominated the crowd that marched to the capital's main square, chanting slogans like "Pena Out," "Fraud, Fraud" with banners decrying what the protesters called the "imposition" of the PRI candidate on Mexico.

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