Ahn Cheol-soo of the minor opposition People's Party(PP) conceded defeat to Oh Se-hoon of the main opposition People Power Party(PPP), making Oh the official pan-opposition candidate for the April 7 Seoul mayoral by-election.

In a statement on Tuesday, Ahn said he acknowledges and accepts the outcome of the two mobile polls as the choice of Seoul residents, before vowing to work hard to help the unified opposition bloc win the election.

While neither camp revealed the details of the outcome due to election laws, Oh reportedly led the polls outside the margin of error.

Ahn, who had previously pledged to seek a merger with the PPP to solidify the opposition's chances in the by-election and next year's presidential race, is scheduled to outline his position and plans later on Tuesday.