(CNN) -- Colombians cast ballots in a hotly contested presidential vote on Sunday, but none of the five candidates running received enough support to win the election.
In the preliminary tally, Oscar Ivan Zuluaga was in the lead with 29.3% of votes, officials said, while incumbent President Juan Manuel Santos had secured 25.6% of votes.
To win a presidential election, Colombian law requires a candidate to obtain more than 50% of votes. That means Zuluaga and Santos will face off in a runoff election on June 15.
A key question voters are weighing: Should Colombia's government keep negotiating with leftist guerrillas or force them to surrender?
Santos was first elected in 2010 on a platform of continuing an offensive against the Revolutionary Armed Forces of Colombia, or FARC, leftist guerrillas that have been at war with the government for decades.
But since late 2012, peace talks with the group have become a hallmark of his presidency.
On Sunday, Santos said that in the second round, voters will choose "between the end of the war and a war without end."
"We are going to choose between those who respect the opposition and the free press, and those who prefer intolerance," he said.
Zuluaga has called for an end to the peace talks and is against giving any political space to the rebels.
On Sunday, he stressed that he also wanted peace for Colombia.
"Peace, yes, but peace that benefits the people," he said. "My pledge is to work for a serious, responsible and lasting peace."
"The difference regarding the candidates' position in the economy and other issues is minimal, but when it comes to how to handle the guerrilla, it's abysmal," pollster Javier Restrepo told CNN last week. "Santos is advocating for a continuation of the peace talks he started in 2012, while Zuluaga's position is that there should not be a dialogue with an illegal guerrilla until its fighters surrender to government forces and lay down their weapons."
Election observers from the Organization of American States said there was a high level of abstention in Sunday's vote, with around 60% of eligible voters deciding to stay home rather than cast ballots, CNN en Español reported.
As candidates debated the issues, a scandal involving a hacker and a video sent shockwaves through the final days of campaigning last week.
The video published by the weekly news magazine "Semana" in Bogotá allegedly shows Zuluaga getting secret military information from a man who was arrested earlier this month and accused of illegal hacking activities.
Zuluaga told reporters the five-minute video was "a vulgar montage" put together to smear his campaign.
CNN's Mariano Castillo and CNN en Español contributed to this report.