Mexico's Lopez Obrador not ready to concede election
The second-placed candidate in Mexico's presidential election has refused to concede, saying his opponent broke electoral rules.
With almost all votes counted, Andres Manuel Lopez Obrador is six points behind the presumed President-elect Enrique Pena Nieto.
Mr Pena Nieto thanked voters for giving his party, the PRI, another chance and vowed no return to the past.
But Mr Lopez Obrador has not ruled out challenging the result.
"I cannot accept any results, until I have complete certainty that the citizens' vote was respected, and the election was not falsified," he told a news conference on Monday.
He said the electoral process had been neither fair nor clean, and the election was "rife with irregularities".
He accused the Institutional Revolutionary Party (PRI) of spending more than their allotted electoral budget.
Mr Lopez Obrador, the candidate of the Party of the Democratic Revolution (PRD) and former mayor of Mexico City launched months of street protests in 2006 after losing the last election to Felipe Calderon by less than one percentage point.
With nearly 99% of the votes counted, Mr Pena Nieto had 38.15% and Mr Lopez Obrador 31.64%, preliminary official results showed.
Josefina Vazquez Mota, the candidate of Mr Calderon's governing National Action Party (PAN), took 25.4% and has already accepted defeat.
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.
Writing in the New York Times on Tuesday , Mr Pena Nieto reiterated that 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 President Felipe Calderon deployed troops against the gangs in late 2006.
His administration would tackle organised crime and drug trafficking, Mr Pena Nieto wrote, 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".
Mr Pena Nieto had been presented as the new face of the PRI, a break with the party's long and at times murky past that included links with drug gangs.
Mr Pena Nieto built his reputation on the "pledges" he set out for his governorship in the State of Mexico, focusing on public works and improvement of infrastructure.
Outgoing President Felipe Calderon congratulated Mr Pena Nieto and promised to work with him during the transition to his inauguration in December for a single six-year term.