"I am sincerely sorry and apologize to the people who must have been very surprised. I will not avoid legal and political responsibility related to this martial law declaration," Yoon said in a televised public address.
He vowed to leave all decisions, including his term, to his People Power Party to decide in order to stabilize the nation, the report said.
The National Assembly of the Republic of Korea is expected to open a plenary session at 5 p.m. Saturday (8 a.m. GMT) to vote on the impeachment of President Yoon Suk-yeol, who is accused of an attempt to violently seize power and abuse of office by imposing martial law without due grounds and in violation of the law.
The leader of the ruling People Power Party (PPP), Han Dong-hoon, said Saturday it has become inevitable for President Yoon to step down early.
"An early resignation [of Yoon] is unavoidable," Han said as quoted by Yonhap.
He said the president is no longer in a position to effectively perform his duties.
The leader of the ruling People Power Party of South Korea, Han Dong-hoon, and Prime Minister Han Duck-soo are holding an emergency meeting following an appeal from President Yoon Suk-yeol, Yonhap news agency reported.