Mexican election winners say runner-up used illegal funds

Mexico's President-elect Enrique Pena Nieto smiles during a news conference in Mexico City July 18, 2012.

MEXICO CITY (Reuters) - Mexico's Institutional Revolutionary Party, or PRI, winner of the July 1 presidential election, on Monday accused the leftist runner-up of exceeding spending limits and using illegal funds to finance his bid.

The allegations were a tit-for-tat exchange after leftist Andres Manuel Lopez Obrador challenged the 3.3 million-vote victory by the PRI's Enrique Pena Nieto. Lopez Obrador alleges the PRI resorted to money laundering and vote-buying to win.

PRI officials fired back on Monday, saying Lopez Obrador's campaign spent 1.2 billion pesos ($88.65 million) more than was allowed in the presidential campaign.

"We have information that public funds were siphoned into the campaign of Andres Manuel Lopez," PRI Chairman Pedro Joaquin Coldwell told reporters at a news conference.

Joaquin Coldwell suggested the funds were likely illegally channeled from the budget of cities and states run by the leftist parties backing Lopez Obrador's presidential bid.

The PRI's counterpunch followed three weeks of allegations from Lopez Obrador, including a broadside on Wednesday that the PRI laundered money to fund vote buying ahead of the election.

Though legal experts doubt Lopez Obrador can overturn the election results in court, the charges have sullied Pena Nieto's victory and added fuel to popular protests against his win.

The PRI ruled Mexico for most of the 20th century, mixing patronage, corruption and outright vote rigging until the party was ousted from the presidency in a 2000 election.

Lopez Obrador, a former mayor of Mexico City, lost the 2006 race to President Felipe Calderon by less than 250,000 votes. Following that defeat, he also contested the results and led massive demonstrations that choked the capital for weeks.

In the aftermath of his protests, Lopez Obrador traveled around the country to drum up support ahead of this year's race.

The PRI's allegations center on the funds used to back Lopez Obrador during this period. The PRI raised similar accusations during the election, which Lopez Obrador's campaign rejected.

(Reporting by Michael O'Boyle; Editing by Lisa Shumaker)