Leftist presidential candidate Andres Manuel Lopez Obrador's campaign should be investigated for using grassroots organizations as "parallel structures" to evade campaign finance rules, Mexico's Institutional Revolutionary Party, or PRI, said.

Both the leftist Progressive Movement and its presidential candidate received funds that they hid from election officials, "triangulating them via grassroots organizations, such as Austeridad Republicana and Honestidad Valiente, among others," PRI leaders said in a press conference on Monday.

The Progressive Movement committed fraud to evade inquiries about the origin and destination of its funds, violating campaign spending limits and hiding its expenses, PRI chairman Pedro Joaquin Coldwell said.

Information obtained by the PRI "allows us to confirm the diversion of public funds to the campaign of Andres Manuel Lopez Obrador from government entities run by members of the Progressive Movement coalition," Coldwell said.

"This is a serious matter, this is not something made up. There are serious legal violations that have led us to conclude that Lopez Obrador is a lamp in the street and darkness at home in terms of legality and transparency," the PRI chairman said.

PRI candidate Enrique Peña Nieto won the presidential election with 38.21 percent of the vote, while Lopez Obrador took second place with 31.59 percent, according to the final official results released by the Federal Electoral Institute, or IFE.

Lopez Obrador, who was the candidate of a coalition of leftist parties led by the Party of the Democratic Revolution, or PRD, filed a challenge earlier this month to the election results, alleging that the PRI engaged in vote buying.

The PRI filed a complaint on June 8 with the IFE regarding the sources of financing of the Honestidad Valiente group, as well as raising questions about the organization's structure and who its funds were going to, Coldwell said.

The PRI plans to appear before the IFE on Tuesday to "reiterate its demand that an extensive investigation be conducted and a report be presented to the session of the general council (of the elections agency) this Thursday," Coldwell said.

Congressman Jesus Murillo Karam, who was recently named legal coordinator for President-elect Peña Nieto, said the left had unreported spending of 1.2 billion pesos (about $88 million).

"Several organizations were formed illegally and we have detected that some governments granted contracts to Austeridad Republicana, which transferred them to Honestidad Valiente, where members of Lopez Obrador's staff were on the payroll and their expenses were paid," Murillo Karam said.

"It was a media stunt based on lack of solid proof," Coldwell said in response to a question about allegations made by the PRD and the conservative National Action Party, or PAN, that the PRI used illegal funds channeled via Monex bank.

The PRD and PAN announced last Thursday that they planned to jointly file a complaint with the Attorney General's Office on alleged money laundering by the PRI.

The two parties also filed a request with the IFE for a speedy investigation of allegations of irregular use of campaign funds by the PRI, which governed Mexico from 1929 to 2000.

The TEPJF electoral court has until Aug. 31 to issue a ruling on the challenge filed by Lopez Obrador's Progressive Movement coalition, either certifying Peña Nieto the winner or calling for a new vote. EFE