By Julia Symmes Cobb and Peter Murphy
BOGOTA, May 29 (Reuters) - Colombia's Oscar Ivan Zuluaga, who faces President Juan Manuel Santos in a run-off vote on June 15, on Thursday backed away from a threat to end peace talks with Marxist rebels if elected, softening his stance on the election's most pivotal issue.
Zuluaga, who won the most votes in a first round of voting on Sunday but not enough to avoid a run-off, is now neck and neck with Santos, a poll showed on Thursday, raising the suspense in the Andean nation's tightest election in years.
The right-wing Zuluaga told Caracol radio that if elected, he would still demand that the Revolutionary Armed Forces of Colombia, or FARC, cease combat and criminal activity to continue the talks Santos initiated in late 2012, but would no longer immediately suspend talks as he promised previously.
Zuluaga did not say how long he would give the FARC to declare a ceasefire, a condition it has rejected until now, but said he softened his stance at the request of Conservative Party leader Marta Lucia Ramirez in exchange for her support in the run-off vote campaign.
"We maintain our same conditions to advance the search for a negotiated peace," Zuluaga told local radio. "We'll allow the talks to continue." He added he would review what had been agreed upon so far during the closed-door discussions.
The question of how to end the country's 50-year conflict, during which 220,000 people have been killed, has been the campaign's most prominent issue, with advancing negotiations appearing to put peace within closer reach than ever before.
Negotiators at the talks, which are being held in Cuba, have reached partial accords on three of five topics under discussion, including land reform, political participation by the FARC and the rebels' withdrawal from the drug trade.
Santos says this election is a choice between grasping a historic chance to end the decades-old conflict by voting for him, or continuing "an endless war" by choosing his rival.
Zuluaga, backed by popular ex-President Alvaro Uribe, who decimated rebel ranks with a relentless U.S.-backed military onslaught, has been critical of the talks with "terrorists" and drug traffickers.
Santos told Caracol radio that Zuluaga's warming to the idea of talks was hypocritical, branding it "politicking."
"Now it turns out they are friends of peace and for continued negotiations, even though they impose conditions impossible to fulfill," Santos said.
The first voter poll since Sunday's first round, published on Thursday by researcher Cifras y Conceptos, showed Santos had a narrow lead of 1 percentage point over Zuluaga, with 38 and 37 percent of voter intentions, respectively, in a survey of 1,672 respondents.
The poll's 2.9 percentage point margin of error means the two candidates are locked in a technical tie. (Additional reporting by Luis Jaime Acosta in Bogota; editing by Matthew Lewis)