SEOUL, Aug. 26 (Yonhap) -- Embattled Seoul Mayor Oh Se-hoon announced his resignation Friday, saying he would take responsibility for his failed attempt to block the free lunch program in a referendum earlier this week.

The decision came two days after the vote on the opposition-led free lunch program was nullified due to a low turnout. The second-term mayor had promised to quit if he failed to stop what he called "welfare populist" policy.

"Today, I resign from the mayoral duty, assuming responsibility for the referendum results," Oh said in a nationally televised news conference. "I want to fulfill my responsibility by quitting now to minimize the political debates and administrative vacuum. I think this is in accordance with the will of the people."

Oh stressed that excessive welfare is bound to bring about an increase in taxes and place a heavy burden on the next generation.

"In light of my resignation, I hope debates on excessive welfare will have more depth and intensity," he said.

A by-election will be held on Oct. 26 to elect Oh's successor.

Until then, Deputy Mayor Kwon Young-gyu will be in charge as an acting mayor, officials said.

The 50-year-old telegenic mayor was once considered one of the presidential candidates for the 2012 race. Back in 2004, then-GNP lawmaker Oh won praise for spearheading strict political donation bills and demanding that senior politicians, who served under the past authoritarian administrations, step back from the frontline of politics.

The biggest issue now is who will take the empty seat in the upcoming by-election, which is seen as a litmus test of public sentiment ahead of the parliamentary elections next April and the presidential vote in December 2012.

If the ruling party loses the seat to the opposition party, political analysts say it could deal a serious blow to the GNP, especially in the Seoul metropolitan area.

Wary of the possible impact on legislative activities in the parliamentary sessions set to open in September, GNP leader Hong Joon-pyo expressed displeasure about Oh's "unilateral decision" to leave office earlier than expected.

"Putting personal reputation ahead of the interests of the nation and party is not desirable as a party member and a member of an organization," Hong said in a party meeting. "I am disappointed about that."

The GNP had initially took some distance with Oh's push for a referendum, playing it down as a policy vote on the city's administrative affairs. As the controversial vote spilled into national-level politics as a welfare battle, the conservative party provided support for the campaign, though some legislators in favor of expanded welfare remain lukewarm.

The main opposition Democratic Party (DP), which called for Oh's immediate resignation, withheld direct comments on Friday's announcement.

"In light of the victory in the free lunch vote, we have to follow people's order with a more humble attitude," DP leader Sohn Hak-kyu said in a senior party meeting. "We have to make an audacious move to push for a universal welfare program and economic democracy with more confidence."