Leftist candidate Andres Manuel Lopez Obrador on Monday refused to concede Mexico's presidential election, calling the apparent victory of his rival Enrique Pena Nieto "fraudulent."

Former Mexico City mayor Lopez Obrador finished second in the presidential election, coming around six percentage points higher than polls had predicted, with 31 percent of ballots cast. Nieto, the former governor of Mexico State, won the election with 38 percent of the vote.

Josefina Vazquez Mota of outgoing President Felipe Calderon's conservative National Action Party (PAN) came in third place with 25 percent.

"We cannot accept a fraudulent result, nobody can accept that," Lopez Obrador said at a press conference in Mexico City, calling Sunday's vote "filthy." He has alleged that Nieto exceeded campaign funding limits, bought votes in some states and took advantage of favorable media coverage.

"We will provide evidence for these claims and will file appropriate legal action," the leftist candidate added.

In 2006, Lopez Obrador lost the presidential election to conservative Felipe Calderon of the PAN by less than 1 percent. He rejected the results as fraudulent, and supporters of his Democratic Revolution Party (PRD) took to the streets of Mexico City in two months of protests.

PRI congressional majority unlikely

Nieto's apparent victory was not as overwhelming as expected. Although his Institutional Revolutionary Party (PRI) will take the presidency, it is unlikely to forge a majority in Mexico's congress.

The PRI coalition with the Green Party got around 38 percent of the congressional vote, with 95 percent of ballots counted Monday. The coalition won about 46 percent of seats in the legislature three years ago.

U.S. President Barack Obama called Nieto on Monday to congratulate him for his victory, saying that he "looks forward to advancing common goals, including promoting democracy, economic prosperity, and security in the region and around the globe in the coming years."

Return of the old guard

PRI monopolized Mexican politics from 1929-2000, and was notorious for corruption and rigging elections. The conservative PAN defeated PRI in 2000, ushering in the first political transition in 70 years in Mexico. PRI was subsequently written off as dead, coming in third in the 2006 election.

The party's comeback has raised concern among many Mexicans, who fear that the it has not truly reformed. But Nieto claims that the PRI is now a democratic party.

"There is no return to the past," Nieto said. "I am going to be a democratic president, who understands the changes the country has undergone in recent decades."

Nieto has promised tax, energy and labor reforms. He has also said he would launch targeted strikes against Mexico's drug cartels. Some 50,000 people have died in Mexico's drug war since outgoing President Calderon deployed troops in 2006.

slk/sad (AP, Reuters)