A fiery leftist promising a war on poverty was in a dead heat with a Harvard-educated conservative in Mexico's presidential election on Sunday, raising fears a contested result could split the country.
Luis Carlos Ugalde, the country's top election official, said it was impossible to separate the leading candidates and there would be no result until at least Wednesday.
"The gap between the first and second place is very narrow, and so it is not possible to announce the winning candidate," Ugalde said in a national televised address.
Exit polls said it was a neck and neck race between Felipe Calderon of the ruling National Action Party and Andres Manuel Lopez Obrador, the left-wing former mayor of Mexico City.