Mexico's right- and left-leaning parties on Thursday jointly demanded authorities investigate an alleged money laundering in financing the campaign of president-elect Enrique Pena Nieto.

Leaders of the ruling National Action Party (PAN) and the leftist Democratic Revolution Party (PRD) said Pena Nieto of the center right Institutional Revolutionary Party (PRI) spent millions of US dollars derived from money laundering to secure his victory.

"We have asked relevant bodies to take this application to resolve and clarify it before the Federal Electoral Tribunal (Trife) issue the ruling of the electoral process before Sept. 6," said PAN's President Gustavo Madero said in a joint press conference with PRD's President Jesus Zambrano.

Madero said the two parties called on Mexico's attorney general to investigate into the alleged voting fraud and had filed a petition to the Federal Electoral Institute (IFE) to "resolve and clear up the issue as quickly and thoroughly as is required."

Final tally released on July 6 by the IFE showed Pena Nieto claimed victory with 38.21 percent of the vote, followed by PRD's Andres Manuel Lopez Obrador with 31.59 percent of the vote, and PAN's Josefina Vazquez Mota with 25.41 percent.

Madero said that when referring to money laundering, it did not necessarily imply that the source of funds was from organized crime, but it might be tax evasion or illegal use of public funds or private. "This is a crime as money laundering," he insisted.

Madero said his party wanted to get to the bottom of the case involving an alleged vote buying by using prepaid cards.

"We are confident that there is strong evidence here, forceful, illegal resource management during this campaign," he said.

The PRD's Zambrano said there was verified proof that illegal funds were funneled to ghost companies campaigning on Pena Nieto's behalf in several states, and that there were links between the companies and the maker of pre-paid gift cards that were used to buy votes.

However, the PRI dismissed the allegations of using illegal proceeds or exceeding campaign caps and announced the party had submitted documents to the attorney general.

At a press conference, PRI's President Pedro Joaquin Coldwell said the attorney general required extensive research and checked the "false accusation."

"They should punish those that are using lies as an instrument of political propaganda," he said, adding that there has been a huge inconsistency in the charges of the PRD.

The PRD and its coalition partners, the Workers' Party and the Citizens Movement, have asked to annul the results of the July 1 presidential election given the gravity of the charges.

The PRD's candidate Lopez Obrador was defeated in 2006 by incumbent President Felipe Calderon by a mere 0.56 percent margin, and thousands of his supporters had blocked the center of the capital for months after he denounced fraud in the election.

The IFE delayed the announcement of the election results because of the vote-buying allegations. The final results will be announced before Sept. 6 and the new president is expected to take office on Dec. 1.