With the upcoming Seoul mayoral election only one month away, unifying the candidacies of two rivals from the opposition bloc remains a key factor in shaping the outcome of the high-stakes election.

The capital Seoul, home to nearly 10 million of the country's total 52 million population, is set to pick its new mayor in the by-election slated for April 7.

The by-election was called after former mayor Park Won-soon died in an apparent suicide in July last year in the face of sexual harassment accusations raised by a former female secretary.

As the highest-profile election held about a year ahead of the 2022 presidential race, the mayoral election is being closely watched as a critical barometer of public support.

Last week, three leading Seoul mayor hopefuls won primaries to qualify to run in the April election -- ex-Startups Minister Park Young-sun of the ruling Democratic Party (DP), ex-Seoul Mayor Oh Se-hoon of the main opposition People Power Party (PPP) and former presidential candidate Ahn Cheol-soo, leader of the minor opposition People's Party.

Running on shared election campaign platforms critical of President Moon Jae-in's progressive administration, conservative opposition candidates Oh and Ahn face a daunting task of unifying their candidacies in the runup to election day.

Recent opinion polls show ruling party candidate Park, when pitted against Ahn, currently the front-running opposition candidate, in a hypothetical two-way race, is neck and neck with him, a clear indication that an opposition victory might be elusive without the unification of the opposition candidacies.

Many agree that achieving a single candidacy for the broader opposition bloc may dictate its chances of winning the upcoming election.

Both Oh and Ahn are eager to start negotiating a single candidacy soon. Nonetheless, a bumpy road lies ahead over how to choose a single candidate, as the PPP appears to be increasingly wary about the possibility of losing to Ahn and being unable to field its own mayoral candidate as the biggest opposition party.

One of the most salient disputes stems from interim PPP chief Kim Chong-in's claim that Ahn, if he wins a primary against Oh, should join the main opposition party and run in the election, bearing the flag of the party. Ahn remains adamant about his objection to the offer.

The two have until March 19, the deadline for registering official candidacies for the election, to settle the single candidacy issue.

DP candidate Park is also on her way to compete with two other candidates from outside the party -- Rep. Cho Jung-hun from the Transition Korea party and Kim Jin-ai of the Open Democratic Party -- to select a single candidate for the broader liberal bloc, but she is highly likely to land her victory there.

"By becoming one team with the Moon Jae-in administration and the DP, (I) will stably (run the city) to return happiness to Seoul citizens," Park said in her acceptance speech after winning the party primary last Monday.

Park, however, faces a more challenging task of overcoming the moral stain the ruling party sustained over the sexual harassment scandal surrounding late former Seoul Mayor Park, who was affiliated with the party.

How to rein in skyrocketing housing prices in Seoul poses another difficult policy challenge to Park as well as her election rivals, after the Moon government has come under a public backlash for soaring housing costs.

In his acceptance speech following his primary victory Thursday, Oh said the upcoming election should serve as a "reckoning" for the Moon government. "This election needs to be one that makes a stern judgment against the reckless Moon government so that a message of warning from the depth of people's hearts will be nailed to the president's chest," he said. "Unless the entire opposition bloc joins efforts, this election will be very difficult to win against the ruling party," Ahn said after winning a separate primary against independent lawmaker Rep. Keum Tae-sup last Monday.

The winner of the upcoming Seoul mayor election will serve out the remaining 14 months of the predecessor's four-year term.

On April 7, Busan, the second-biggest South Korean city, is also going to vote for a new mayor in a by-election after former mayor Oh Keo-don stepped down in mid-2020 in the face of sexual harassment allegations. He was indicted in January on charges of sexually abusing two of his female subordinates while in office.(Yonhap)