Oh Dong-woon, chief of the Corruption Investigation Office for High-ranking Officials, speaks at the Legislation and Judiciary Committee meeting at the National Assembly in Seoul, Monday. Yonhap

President Yoon Suk Yeol was banned from leaving the country, Monday, as investigative authorities requested the travel restriction, a measure typically imposed on suspects in high-profile crimes, in relation to their investigation into his unconstitutional, short-lived martial law.

This is the first time such a ban has been imposed on an incumbent president of Korea for any reason. Yoon is currently under investigation as a suspect for treason and abuse of power.

Oh Dong-woon, the chief prosecutor at the Corruption Investigation Office for High-ranking Officials (CIO), informed the National Assembly's Legislation and Judiciary Committee on Monday that he had instructed investigators to apply for the overseas travel ban to the justice ministry, which subsequently accepted the request.

Such a ban is imposed on individuals whose departure from the country could disrupt a criminal investigation.

Regarding the possibility of arresting Yoon, Oh said it is the "principle of investigation to arrest the prime suspect of treason," but he did not elaborate on whether they are considering arresting the head of state.

Earlier in the day, the National Office of Investigation (NOI) at the National Police Agency, which is also probing the martial law case, said it was also considering imposing the travel restriction on Yoon.

Regarding the possibility of placing Yoon under emergency detention, an official at the NOI said, “It is possible if it meets the requirements. However, we must first review whether his case satisfies those conditions.”

An emergency detention is implemented when a suspect, believed to have committed a serious crime, is likely to destroy evidence or flee. The suspect can be detained without an arrest warrant, but investigative authorities must obtain an official warrant from a court within 48 hours.

Woo Jong-soo, chief of the National Office of Investigation, speaks during a press conference at the Korean National Police Agency in Seoul, Monday. Yonhap

The NOI said travel bans had already been imposed on four senior government and military officials involved in the martial law operations — former Defense Minister Kim Yong-hyun, believed to be the mastermind behind the martial law plan, former Interior Minister Lee Sang-min, Lt. Gen. Yeo In-hyung, and Army Chief of Staff Gen. Park An-su.

“There are no restrictions to the subject of the investigation. We will conduct a strict investigation in accordance with laws and principles, without any exceptions,” Woo Jong-soo, the chief of the NIO, said.

Currently, all relevant probe authorities — the CIO, the NOI and prosecutors — are each handling Yoon's case.

Earlier in the day, the CIO vowed to take the lead in the investigation and requested the police and prosecution to transfer their ongoing cases to them, citing concerns over fairness.

"We requested the police and prosecutors to transfer their ongoing probe cases considering the fact that their investigations may be affected by their relationship with power. As an independent investigative authority, we will thoroughly uncover the truth in line with laws and principles," Lee Jae-seung, deputy director of the CIO, said in a press briefing.

On Sunday, prosecutors said they have begun investigating Yoon in accordance with due procedures, following multiple complaints filed against him.

However, some pointed out that prosecutors should be excluded from the investigation, considering their relations with Yoon who was also a former prosecutor.

“The prosecution, which played an instrumental role in the launch and retention of Yoon's ‘prosecution-led government,' now claims it will investigate the president on treason charges. Charges of insurrection are not within the scope of the prosecution's investigative power. Leave the case to the NOI and CIO and keep your hands off,” said Cho Kuk, a law professor-turned-leader of the minor opposition Rebuilding Korea Party.

Reps. Kim Yong-min, right, and Kim Seung-won of the main opposition Democratic Party of Korea, submit two bills mandating special counsel probes into President Yoon Suk Yeol's martial law declaration and first lady Kim Keon Hee's corruption allegations, at the National Assembly in Seoul, Monday. Yonhap

Meanwhile, the main opposition Democratic Party of Korea (DPK) put forward a proposal for a special counsel to investigate the allegations of treason and abuse of power against Yoon.

A separate motion to appoint a permanent special counsel to investigate the treason charges has been approved by the Legislation and Judiciary Committee. The DPK plans to bring the bill to a vote at the plenary session on Tuesday.

The DPK also proposed a bill mandating a special counsel investigation into allegations involving first lady Kim Keon Hee, including suspicions of involvement in a stock manipulation scheme and interference in election nominations through a power broker. This is the fourth version of the bill targeting the first lady, following a similar proposal vetoed by Yoon last month, which was ultimately discarded in a revote on Saturday.

The DPK also reiterated its call to deprive Yoon of his power to command the military due to fears of him declaring martial law again. Yoon remains in command of the military, according to the Ministry of National Defense.

President Yoon Suk Yeol clears his throat during a press conference at the presidential office in Yongsan District, Seoul, Nov. 7. Yonhap