Park Young-sun, the ruling party candidate for April's Seoul mayoral by-election, called opposition bloc candidate Oh Se-hoon an outdated mayor who failed, while referring to herself as a mayor for the future.

Speaking to reporters after visiting Choe Kang-wook, the head of the minor Open Democratic Party, Park at one point also called Oh a "liar."

Kang Sun-woo, the spokesperson for Park's camp, referred to Oh stepping down as Seoul mayor in 2011 after losing the free school lunch referendum, accusing him of abandoning his duty and habitually lying.

The ruling Democratic Party continued to ramp up pressure against Oh to clarify allegations that he included land owned by his in-laws in the Seoul city's development project during his term as mayor for monetary compensation.