[JURIST] Mexican leftist presidential candidate Andres Manuel Lopez Obrador [campaign website, in Spanish; Wikipedia profile] told reporters in Mexico City Saturday ahead of a mass rally that voting fraud caused his official loss to ruling party candidate Felipe Calderon [campaign website, in Spanish; Wikipedia profile] in the July 2 presidential election, and once again declared he would contest the result [JURIST report]. Obrador, leader of the Democratic Revolution Party [party website, in Spanish], said he could mathematically prove that the electronic counting system that provided televised results was manipulated despite assurances from a team of European Union observers that there was no evidence of fraud. The Federal Electoral Institute (IFE) [official website, in Spanish] has also validated the results. Last week's recount of polling station tally sheets resulted in a margin of victory of one percentage point for Calderon, prompting Obrador to demand a full manual recount [JURIST report] in a challenge filed with the Electoral Tribunal of the Federal Judiciary [official website, in Spanish]. Mexican election laws [PDF text, in Spanish] permit a manual recount only if the ballot packages have been unsealed or if the initial tallies are faulty.

The Electoral Tribunal must make a decision on Obrador's challenge by August 31. The results of the election must be certified by September 6. Reuters has more.