SEOUL - South Korea's joint investigation unit said Monday that it sought a warrant to arrest the impeached President Yoon Suk-yeol over his martial law imposition.

The investigation unit, consisting of Corruption Investigation Office for High-ranking Officials, National Office of Investigation and the defense ministry's investigation headquarters, said in a short notice that it requested the arrest warrant for Yoon at midnight to the Seoul Western District Court.

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It marked the first time in the country's modern history that an arrest warrant has been filed against an incumbent president.

The unit asked Yoon to appear for questioning three times on Dec 18, Dec 25 and Dec 29, but Yoon's side refused to receive summons while having yet to submit documents for the appointment of his defense counsel.

Yoon, who was named by investigative agencies as a suspected ringleader on insurrection charge, will submit a written opinion and appoint defense counsel to the Seoul Western District Court, Yonhap news agency reported, citing Yoon's side.

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Yoon Kab-keun, lawyer and former prosecutor, was quoted as saying that Yoon's written opinion will be submitted later in the day to the court. The lawyer noted that the appointment letter for Yoon's defense counsel will be delivered to the court.