Mexican presidential candidate Andres Manuel Lopez Obrador has called for a ballot-by-ballot review of Sunday's presidential vote. He says the stability of the country is at stake.

Mexico's Federal Electoral Institute Wednesday began reviewing the totals from polling stations to determine whether Obrador's rival, Felipe Calderon, really won the election Sunday. A preliminary count showed him ahead by only one percentage point. Both candidates declared victory Sunday night.

Election officials said late Tuesday that Calderon's lead narrowed to less than a percentage point after they counted 2.6 million votes left out of the original total because of errors on the ballots.

Party representatives may challenge the election results in court once the Federal Electoral Institute releases the figures. Lopez Obrador has said his party is ready for a legal battle.

Some information for this report was provided by AFP, AP and Reuters.