South Korea's two left-leaning presidential hopefuls agreed Tuesday on a potentially game-changing merger to field a single candidate against conservative front-runner Park Geun-Hye.
Moon Jae-In from the main opposition Democratic United Party and Ahn Cheol-Soo, a software mogul running as an independent, agreed on the merger at closed door-talks in Seoul, officials from their respective campaigns said.
However, there was no immediate decision on which one would drop out of the race in favour of the other, the officials told reporters, adding that a final announcement would be made in the coming weeks.
Both men had come under growing pressure before the December 19 ballot to merge and avoid splitting the liberal vote, which would effectively hand the presidency to Park who has a lock on the sizeable conservative bloc.
"It was agreed that officials from both sides will meet soon to prepare a joint declaration on broad political reforms," Ahn's spokesman told AFP.
"After the declaration is completed the two candidates will reach a decision on who will run as a single candidate."
Polls suggest Park from the ruling New Frontier Party would easily win in the event of a three-horse race, but they put her neck and neck in a face-off with either Moon or Ahn.
Moon's camp had been especially vocal on the need for a unified candidacy. Ahn's side has been more cautious, insisting on a commitment from Moon's party to political reform.
Ahn has virtually no political experience but is enormously popular with young liberal voters, who see him as untainted by corruption or by political or commercial abuse of power.
Although courted by politicians across the political spectrum, he has remained without party affiliation despite an obvious empathy with the liberal opposition.
Ahn has repeatedly attacked predatory capitalism and called for the overhaul of an economy dominated by a few powerful conglomerates known as "chaebol".
Moon's supporters argue that their man would make the better candidate as he has the party base and political experience necessary for the president in dealing with parliament.
Moon, a human rights lawyer and former pro-democracy activist, is best known for serving as a top aide to then-president Roh Moo-Hyun, who committed suicide in 2009.