MEXICO CITY (Reuters) - The head of Mexico’s leftist National Regeneration Movement (MORENA) party, Andres Manuel Lopez Obrador, called on Tuesday for a recount of Sunday’s key State of Mexico gubernatorial election.

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With nearly 98 percent of returns in from polling booths, the candidate for President Enrique Pena Nieto’s Institutional Revolutionary Party (PRI), Alfredo del Mazo, had 34 percent of the vote compared with 31 percent for MORENA’s candidate, Delfina Gomez.

“MORENA believes that Delfina Gomez won the election on Sunday and that she is the governor of the State of Mexico,” said Lopez Obrador.

The election was tarnished by piles of pig heads dumped on Saturday near MORENA offices and at polling stations in several municipalities, and accusations of telephone threats and fake electoral literature warning of attacks - tactics used to dissuade people from voting. Prosecutors are probing the situation.

“We do not accept any result derived from electoral fraud, nor will we recognize any authority arising from the violation of constitutional principles,” said Lopez Obrador.

“As of today we have asked the electoral institute of the State of Mexico to carry out a recount of votes. We want all votes to be counted, vote by vote, voting station by voting station,” he added.

Lopez Obrador has alleged fraud in past elections.

Known as AMLO, the silver-haired politician earned the ire of many Mexico City residents after the 2006 presidential vote when he brought parts of the capital to a standstill with mass protests, saying he had been robbed of victory by center-right candidate Felipe Calderon.

“When Lopez Obrador loses elections, which is quite often, he never accepts the results. He is a sore loser,” said PRI Chairman Enrique Ochoa.

Ochoa, who often throws verbal jabs at Lopez Obrador, again accused the leftist politician of threatening to turn Mexico into strife-torn Venezuela and said Lopez Obrador had resorted to calling for violence in prior electoral losses.

“We will not be provoked, we won’t give those who are violent reason to accuse us of violence. We won’t fall into that trap,” said Lopez Obrador.

Encompassing many populous neighborhoods on the edge of Mexico City, the State of Mexico is home to one in eight Mexican voters and it has long been a source of strength and financing for the PRI.