A voter casts a ballot during a by-election for an administrative seat at a ballot station in Sadang 2-dong, Dongjak-gu, Seoul, on Wednesday.

The office of President Yoon Suk Yeol vowed Thursday to push for major reform agenda items after the ruling People Power Party won crucial by-elections on its home turf.

The PPP secured victories in its traditional stronghold constituencies -- Busan's Geumjeong District and Incheon's Ganghwa County -- in Wednesday's by-elections as the party seeks to recover from waning approval ratings for both Yoon and the party following its crushing defeat in the April 10 parliamentary elections.

The main opposition Democratic Party won two administrative seats Yeonggwang and Gokseong counties in South Jeolla Province, while Jung Keun-sik, a left-leaning professor, was elected the education chief of Seoul.

"Even if there are challenges, we will unwaveringly push forward with the four major reforms, including healthcare reform and tackling the low birth rate, as we move toward the future," a presidential official said in a press notice.

"We will address any shortcomings by listening to the will of the people and making necessary changes," the official added.

The electoral win in the PPP's traditional strongholds was seen as a boost for party leader Han Dong-hoon, who has had disagreements with Yoon on key issues, including matters related to first lady Kim Keon Hee.

Earlier in the day, Han reiterated his calls for the first lady to withdraw from public activities and urged for a presidential office reshuffle to remove those considered close to Kim and exercising undue influence on state affairs. (Yonhap)