BOGOTA, June 6 (Reuters) - Colombia's President Juan Manuel Santos has gained a lead in a tight June 15 election race over right-wing opposition candidate Oscar Ivan Zuluaga, a poll published on Friday showed, hours after another indicated they were neck-and-neck.
The poll, by researcher Cifras y Conceptos, showed 43.4 percent of respondents would vote for the center-right Santos versus 38.5 percent for Zuluaga in an election campaign that has centered on how to end the country's five-decade civil war.
A separate survey by international researcher Gallup on Thursday evening gave Zuluaga a narrow lead with 48.5 percent versus 47.7 percent for the president, but the pair are effectively tied given the poll's margin of error.
Incumbent Santos is fighting for a second four-year mandate to complete peace talks he initiated with the leftist FARC or Revolutionary Armed Forces of Colombia in 2012. The talks, he says, offer a rare chance to end a war that has killed around 220,000.
Zuluaga wants to impose tougher conditions for those talks in Havana, which would increase the risk of their collapse.
His demands include a FARC ceasefire, strict adherence to a timetable, jail terms for leaders, and an end to the planting of land mines and forced recruitment of children.
While Santos had long been favored to win the election, Zuluaga has won increasing support from voters who question the FARC's willingness to disarm and walk away from the lucrative illegal drugs trade even if a peace deal is signed.
The survey of 3,215 people, carried out from May 31 to June 3 and published in local media, came before Clara Lopez, a leftist candidate knocked out of the race in the first round, endorsed Santos on Wednesday this week. It had a 2.9 percent margin of error.
The percentage who would make a protest or blank vote by voting for neither candidate was 11.7 percent, the poll showed, while another 6.3 percent of voters were still undecided between the two candidates. (Reporting by Peter Murphy; Editing by Chizu Nomiyama)