Yoon shocked the nation and his own ruling People Power Party on Tuesday when he gave the military sweeping emergency powers in order to root out what he called "anti-state forces" and overcome obstructionist political opponents.
He rescinded the declaration about six hours later after parliament, including some members of his party, voted to oppose the decree.
Yoon Suk-yeol shocked South Korea and his own ruling party when he declared martial law on Tuesday. (AP PHOTO)
The main opposition Democratic Party held meetings on Friday to discuss impeachment and has scheduled a vote for Saturday evening.
Speaking after a People Power Party meeting on Friday, leader Han Dong-hoon said Yoon had ordered the arrest of prominent politicians on the grounds they were among those "anti-state forces".
The presidential office denied any such order had been given, the Yonhap news agency reported.
Fearing another attempt to declare martial law, opposition MPs rotated through parliament's plenary session hall to block any such attempt, a Democratic Party official said.
Acting Defence Minister Kim Seon-ho said reports there might be another attempt to impose martial law were not true.
Han said earlier there was "a high risk of extreme actions such as this emergency martial law being repeated" while Yoon remained in power, putting the country in "great danger".
The ruling party's stance against impeachment might be shifting, leader Han Dong-hun said. (AP PHOTO)
On Thursday, the ruling party said it was against impeachment, but Han suggested that stance might be shifting in light of "credible evidence" that Yoon had intended to arrest and detain political leaders at Gwacheon, just south of Seoul.
"I believe that President Yoon Suk-yeol's immediate suspension of office is necessary to protect the Republic of Korea and its people in light of the newly revealed facts," Han said.
He did not explicitly call for impeachment or provide clarification.
Some party members said they did not want a repeat of the 2016 impeachment of then-president Park Geun-hye, which triggered the implosion of the conservative party and a victory by liberals in presidential and general elections.
"We cannot impeach the president tomorrow and hand over the regime to Lee Jae-Myung's Democratic Party," PPP MP Yoon Sang-hyun told reporters.
An impeachment bill would need support from two-thirds of the 300-member assembly, so eight members of Yoon's party would have to side with the opposition for the bill to pass.
Yoon Suk-yeol's declaration stirred painful memories of the country's long years of military rule. (AP PHOTO)
If parliament votes to impeach, the president is suspended from exercising his powers until an impeachment trial is held by the Constitutional Court.
The prime minister serves as leader in acting capacity.
The national police are investigating Yoon and Kim Yong-hyun, the defence minister who allegedly encouraged him to declare martial law and who has since resigned.
Government and military prosecutors are also conducting a joint investigation into the martial law decision.
Details were slowly emerging about the chaos that engulfed Seoul on Tuesday night following Yoon's surprise declaration, which stirred painful memories of the country's long years of military rule following World War II.
Kwak Jong-geun, the special warfare commander, said he defied an order from then-defence minister Kim to drag MPs out of parliament.
A commander said he defied an order to drag MPs out of parliament during martial law. (AP PHOTO)
"I knew it would be disobedience, but I did not order that mission. I told them not to go in," Kwak told an opposition MPs YouTube channel.
Kwak also said he ordered his troops not to carry live ammunition.
Ahn Gwi-ryeong, a spokeswoman for the opposition Democratic Party, said she believed the people had already psychologically impeached Yoon.
Images of Ahn grappling with a soldier and grabbing hold of his gun outside parliament on Tuesday went viral on social media as a symbol of the country's defiance against martial law.
"Who could trust a president declaring martial law almost like a child playing games or entrust the nation to such leadership?" she told Reuters.
Yoon's approval rating plunged to a new low of 13 per cent, according to a Gallup Korea poll released on Friday.
