South Korea's six opposition parties on Wednesday submitted a motion to impeach President Yoon Suk Yeol over the martial law declaration the previous day.

The six parties - the main opposition Democratic Party of Korea, and minor oppositions Rebuilding Korea Party, Reform Party, Jinbo Party, Basic Income Party and Social Democratic Party - plan to put the motion to the plenary session on Thursday, and to put it to the vote on Friday or Saturday.

The main opposition had hinted at such a move hours after opposition parties hinted at proceeding with an immediate impeachment of President Yoon shortly after he agreed to the parliament's request to lift martial law.

A group of over 40 lawmakers from opposition parties declared that the Assembly should impeach Yoon, calling him "the mastermind of a treasonous act of state mismanagement."

Hwang Un-ha, floor leader of the Rebuilding Korea Party, said, "The president committed an act tantamount to treason by mobilizing the military. It is clear that he cannot remain in office even for a moment longer. Therefore, we must urgently pass an impeachment motion."

Hwang urged each party to propose the impeachment motion on Wednesday. Such a motion must be voted on within 24 to 72 hours after its proposal.

"The National Assembly should focus on approving the impeachment as quickly as possible to immediately suspend the president's duties," he said.

Earlier, Democratic Party leader Lee Jae-myung criticized the martial law declaration as unconstitutional and illegal. Speaking to reporters shortly after a National Assembly resolution demanding the lifting of martial law was voted, he said, "President Yoon’s proclamation of martial law utterly failed to meet the substantive requirements stipulated by the Constitution and the Martial Law Act."

"President Yoon has betrayed the people. His illegal declaration of martial law is null and void. From this moment, Yoon Suk Yeol is no longer the president of the Republic of Korea."