Political outsider Abelardo de la Espriella was commanding a thin lead over leftist rival Ivan Cepeda  following the tight presidential vote in Colombia.

On Sunday evening, the country's electoral officials said de la Espriella had 43.7% of the votes and Cepeda 41%, with nearly all of the votes counted.

Neither of them seems on track to clear the 50%-plus hurdle required to secure the presidential post, making it likely for the outcome to be decided in the runoff round.

Commenting on the initial count hours after the polls have closed on Sunday, Cepeda mentioned reports of "atypical voting" and seemed to cast doubt on the preliminary count.

"We will not comment on tonight's results until the vote-counting committees have fully clarified this matter," said Cepeda, who has been leading the polls throughout the campaign.

Outgoing President Gustavo Petro also said he did not except the tally which put his favorite, Cepeda, in second place. Petro pledged to wait for the final results, which will be reviewed by judges.

Colombia: What do the candidates stand for?

The frontrunner Abelardo de la Espriella has has often portrayed himself as a tough crime fighter who also spoke in support of US President Donald Trump. The 47-year-old businessman's campaign style has drawn comparisons with right-wing president of El Salvador, Nayib Bukele.

Ivan Cepeda, a 63-year-old left-leaning senator, has promised to expand social reforms. Incumbent President Gustavo Petro, who cannot legally seek another term, has thrown his support behind Cepeda.

The candidates have been campaigning on promises to tackle armed, drug-running guerrilla groups, reduce inequality and poverty and improve the country's healthcare system — albeit in different ways.

Leftist Cepeda, ​the son of a murdered communist leader, has promised to pursue peace with illegal armed cartels through negotiations, a policy that has led to little progress under Petro. 

De La Espriella has promised a tough offensive against the groups, proposing the construction of 10 "mega-prisons." In addition to his pledge to clamp down on crime, he promised to fight poverty with education, healthcare and social housing.

On poverty and health, Cepeda wants to see wealth distributed more evenly by raising taxes on high earners to fund an expansion of Colombia's healthcare system. He has also proposed gifting 1 million hectares (2.47 million ) of land ​to victims of the country's six-decade internal conflict.

What about Paloma Valencia?

Pre-election polls put Cepeda in a notable lead, and also projected a closer three-way race involving right-wing senator Paloma Valencia, who ended up with less than 7% of the vote.

Valencia had urged tax breaks for companies to create more jobs and lift Colombians out of poverty. She had also proposed additional funding for social programs and healthcare — financed not by taxation but by renewed oil and gas exploration.

Valencia conceded shortly after learning of the result, and said she will support right-wing candidate de la Espriella in the June runoff.

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Edited by: Darko Janjevic