SEOUL -- South Korea's main opposition Democratic Party of Korea said Thursday that it will push for a vote Saturday for an impeachment motion against President Yoon Suk-yeol over his shocking yet short-lived imposition of martial law.

Cho Seung-rae, the main opposition's senior spokesperson, said it plans to hold a vote on the motion at around 7 p.m. local time Saturday to give ruling party lawmakers enough time to deliberate over their decision on Yoon's actions, Yonhap news agency reported.

The Democratic Party, which holds a majority in the 300-seat parliament, has submitted the impeachment motion with the backing of five smaller opposition parties, arguing Yoon's martial law declaration constituted violations of the constitution and other laws.

The vote on the impeachment motion requires a two-thirds majority to pass, which would need eight of the 108 ruling party lawmakers to vote with opposition parties. If it passes, the Constitutional Court would then decide whether to uphold the motion, with a decision required within 180 days.

Han Dong-hoon, leader of the ruling People Power Party, said at a party meeting on Thursday that the unconstitutional martial law order cannot be justified, urging Yoon to leave the party. But he pledged his party will rally efforts to block the motion's passage to avoid confusion.

The floor leader of the People Power party Choo Kyung-ho also vowed Thursday that its lawmakers would "unite" to defeat the opposition-led impeachment motion, which would immediately suspend Yoon's presidential duties.

"President Yoon will not make any statements today," a presidential official told reporters Thursday.

During a meeting on Wednesday with key political figures, including Prime Minister Han Duck-soo, Yoon said there was "no wrongdoing" in the declaration of martial law and dismissed allegations of any impropriety, emphasizing that it was solely intended to prevent what he described as the Democratic Party's "reckless impeachment actions," local media reported.

Several high-profile cabinet ministers have expressed their intention to step down. Earlier on Thursday, Yoon accepted the resignation of his defense minister Kim Yong-hyun and nominated his ambassador to Saudi Arabia, Choi Byung-hyuk, as a replacement, the presidential office said.

Kim, who reportedly proposed to the president declaring martial law, tendered his resignation on Wednesday evening, shortly after the Democratic Party submitted an impeachment motion against him.

The outgoing defense chief said he offered to step down in a bid to take full responsibility for all events related to Tuesday's martial law declaration and apologized to the South Korean people for causing disruption and confusion.

In a further development on Thursday, South Korean prosecutors banned Kim from leaving the country, Yonhap news agency said.

Meanwhile, South Korean police launched an investigation into a case of Yoon's treason charge, a senior police officer said Thursday.

Police have begun investigating the president for alleged "insurrection" following his declaration of martial law and subsequent lifting, which has sparked widespread political turmoil. Woo Jong-soo, head of the National Office of Investigation of the National Police Agency, confirmed that "the case has been assigned."

Yoon shocked the country by declaring emergency martial law Tuesday night, claiming to eradicate "anti-state" forces, only to lift the order six hours later after being rejected by 190 lawmakers in parliament.

On Wednesday night, demonstrators in downtown Seoul held a candlelight vigil and marched towards the presidential office against Yoon, demanding that he step down.