Seoul Mayor Oh Se-hoon will soon announce when he will resign over the failed free lunch vote after consulting with his ruling Grand National Party (GNP) to minimize its negative impact ahead of next year's major polls, his aides said Thursday.

A referendum was held on Wednesday to ask Seoul residents whether they endorsed an opposition-led free lunch program for all, but it was nullified due to low turnout. Mayor Oh had vowed to quit if he failed to stop what he called a "welfare populist" policy through the poll, effectively turning the rare test of public sentiment on welfare spending into a vote of confidence on the conservative mayor.

Now, all eyes are on the 50-year-old Oh as political watchers wait to see when he will leave office and how his decision will affect the political landscape ahead of parliamentary elections next April and a presidential vote in December 2012.

Asked whether he had slept well on his way to work early Thursday, the mayor replied, "How can I have a good sleep?" But he stopped short of saying when he will announce his resignation.

According to his spokesman Lee Jong-hyun, Oh is set to announce his decision on Friday after discussing with party members ways to minimize political uncertainty.

Though GNP floor leader Hwang Woo-yea and chairman Hong Joon-pyo opposed Oh's immediate resignation ahead of the regular parliamentary session, other senior members said an early retreat is inevitable in order for him to keep his word.

The main opposition Democratic Party (DP) put pressure on Oh, urging him to step down right now and take full responsibility for the vote that failed to draw residents' support.

"Oh offered to step down and he sternly said he will resign,"

DP floor leader Kim Jin-pyo said. "As a politician, if he continues to hold office, every single day will be sheer torture for him."

If Oh resigns within the next month, a by-election will be held in October to pick a new mayor, which could be a litmus test on the public sentiment ahead of 2012 elections.

If he stays past September to allow time for a replacement to take over, a by-election will be held next April on the sidelines of the general election, which is less likely to happen considering opposition within the GNP.

If the ruling party loses the seat to the opposition party, political analysts said it could deal a serious blow to the GNP legislators, especially in the Seoul metropolitan area. (Yonhap News)