On Sunday, Gustavo Petro was elected president of Colombia, becoming the country's first leftist leader since the 1930's.
Petro defeated the runner-up, Rodolfo Hernandez, with a margin of 700,000 votes.
Hernandez conceded defeat two hours after the polls closed.
The independent Electoral Observation Mission (MOE) received up to 297 election fraud reports.
Some voters reported they had received tainted ballots, with dots and stripes in the square meant for the blank vote.
These print errors could "confuse" election jurors, who will disqualify votes with marks in more than one of the options on the ballot.
