By Ioan Grillo
MEXICO CITY (Reuters) - Mexico's ruling conservatives on Thursday lent their support to accusations that President-elect Enrique Pena Nieto benefited from laundered money in his campaign, piling more pressure on the country's next leader.
Gustavo Madero, chairman of the National Action Party (PAN) of outgoing President Felipe Calderon, told reporters he was presenting a legal complaint about money laundering to the federal attorney general's office.
"Any money coming from illicit sources can be laundered money,' Madero said. "It could be stolen, it could be from tax evasion, it could be money they have taken from a company, from the government or from state governments."
Madero was speaking at a joint news conference with Jesus Zambrano, chairman of the Party of the Democratic Revolution (PRD), the main leftist grouping behind presidential runner-up Andres Manuel Lopez Obrador, who has led the accusations against Pena Nieto.
The attorney general's office does not have the power to overturn the July 1 election.
However, money laundering charges could damage Pena Nieto, whose win puts the presidency back in the hands of the Institutional Revolutionary Party (PRI). The PRI ruled Mexico from 1929 until 2000, when it was defeated by the PAN.
Pena Nieto won the July 1 election with 38.2 percent of the vote, against Lopez Obrador with 31.6 percent and the PAN's Josefina Vazquez Mota with 25.4 percent.
Lopez Obrador has also legally challenged the vote with the electoral tribunal, accusing Pena Nieto of buying votes and calling for the election to be annulled.
The electoral tribunal has until September to rule on those charges and officially declare Pena Nieto president. It is widely expected to uphold the election.
Pena Nieto, who is due to take office on December 1, has repeatedly denied any wrongdoing and has called his win "categorical." Calderon has congratulated him on his victory, as have dozens of world leaders.
Responding to the joint PAN-PRD announcement, PRI chairman Pedro Joaquin Coldwell dismissed the allegations as unfounded and called on the attorney general's office to bring defamation charges against his party's accusers.
"They should punish those that are using lies as an instrument of political propaganda," he told a news conference.
Lopez Obrador also contested the 2006 election, which he lost by less than 1 percentage point to Calderon and then blocked streets in the capital for weeks in protest.
PRI officials have said that the leftist is simply "a bad loser" protesting two elections in a row.
However, the PAN's allegations add weight to the complaints.
The PRI was widely accused of rigging elections during its 71 year grip on power, so the new accusations of corruption strike a chord with many Mexicans.
(Additional reporting by Lizbeth Diaz; Editing by Dave Graham and David Brunnstrom)