The left-wing runner-up in Sunday's presidential poll in Mexico has said he will demand a total recount of the vote.
"For the good of democracy and of the country, all the votes must be counted," Andres Manuel Lopez Obrador, of the left-wing PRD, told reporters.
He had refused to concede victory after rival Enrique Pena Nieto came first in preliminary results.
Mr Lopez Obrador has accused Mr Pena Nieto of breaking electoral rules.
Earlier on Tuesday, Mr Lopez Obrador, the candidate of the Party of the Democratic Revolution (PRD) and former mayor of Mexico City, had said the electoral process had been neither fair nor clean, and that the election was "rife with irregularities".
With 99% of votes counted, Mr Pena Nieto had a six percentage point lead over Mr Lopez Obrador. The final results are expected on Wednesday.
After losing the 2006 presidential election by a narrow margin to Felipe Calderon, Mr Lopez Obrador launched street protests that lasted for several months.
He has now accused Mr Pena Nieto's Institutional Revolutionary Party (PRI) of spending more than their allotted electoral budget.
Mr Pena Nieto, 45, declared himself the winner of Sunday's presidential election after a preliminary count.
He promised to govern "with and for all", saying he would "honour" the PRI's second chance with "a new style of governing".
The PRI governed Mexico for 71 years, but lost the presidency in 2000.
Mr Pena Nieto reiterated there would be no return to "old ways".
He also addressed Mexico's war on drugs, that has seen more than 55,000 deaths since Mr Calderon deployed troops against the gangs in late 2006.
Mr Pena Nieto said his administration would tackle organised crime and drug trafficking, but there would be a change of strategy and spending on security would increase.
Security efforts "must be married with strong economic reforms. You can't have security without stability," he said.
And other nations, particularly the United States, "must do more to curtail the demand for drugs".