Mexican presidential candidate Andres Manuel Lopez Obrador says he has "irrefutable" video proof of fraud committed by his election rivals.
Mr Lopez Obrador aired the video at his campaign headquarters
The electoral authorities say the video images showing supposed irregularities have been misinterpreted.
Results from the 2 July poll show conservative candidate Felipe Calderon winning by 0.57 percentage points.
Mr Lopez Obrador has filed a legal challenge and called for nationwide protests to press calls for a recount.
Mr Calderon secured 35.88% of the 2 July vote, against 35.31% for Mr Lopez Obrador.
The latter's 900-page lawsuit alleges violations before and during the election.
Mr Lopez Obrador's complaint includes accusations that Mr Calderon overspent on his campaign and claims that there was unfair government support for him.
He also alleges that some polling areas had more votes than registered voters, and that a computer software programme skewed the initial count of votes.
Mr Lopez Obrador has asked the electoral tribunal to order a full manual recount of all the ballots.
He said he would wait to see the court's ruling on his lawsuit before deciding if he would accept it.
The shaky amateur video footage aired at Mr Lopez Obrador's campaign headquarters showed two incidents which he claimed were examples of "old-style fraud". He said that that they had been sent in by some of his supporters.
One tape, filmed in Queretaro state during a recount of votes for the presidential election, showed what seemed to be an election official refusing to recount the ballots in a box which had been declared in favour of Mr Calderon.
The other showed an alleged supporter of Mr Calderon's National Action Party (Pan) apparently stuffing six ballots into a box being used for congressional elections, which were held on the same day as the presidential race.
The Federal Electoral Institute (IFE) said the man was putting some ballots that had been put in the wrong box into the correct box and that this had been witnessed by representatives of all the main parties.
"The images in this video, related with supposed irregularities, have been misinterpreted," an IFE statement said.
"This is just noise making. It is trying to throw the election into the trash can," Cesar Nava, an official from Mr Calderon's party, told a news conference.
The EU said last week its monitors had found no indication of irregularities.
Mr Lopez Obrador's supporters say they intend to visit foreign embassies in Mexico City to demand that their governments do not congratulate Mr Calderon.
A number of international leaders, including US President George W Bush, have already congratulated Mr Calderon on his success.
On Monday, White House spokesman Tony Snow defended Mr Bush's decision to call Mr Calderon on Thursday.
Hesaid that that Mr Bush would, however, respect any Mexican court ruling on who won the election.