President Yoon Suk Yeol delivers a public address at the presidential office in Yongsan District, Seoul, Dec. 12. Yonhap

The joint investigation unit into the martial law turmoil on Monday was attempting to deliver a summons for President Yoon Suk Yeol to appear for questioning this week over his declaration of martial law earlier this month.

The joint team between the police, the Corruption Investigation Office for High-ranking Officials (CIO) and the defense ministry's investigation unit seeks to question Yoon as a suspect on charges of insurrection and abuse of power in connection to the martial law imposition on Dec. 3.

Authorities attempted to deliver the notice to the presidential office for Yoon's appearance Wednesday, but the office declined to cooperate, citing the suspension of Yoon's duties after his impeachment by the National Assembly on Saturday.

The team later sent a team to Yoon's residence to deliver the summons request. In the document, Yoon is reportedly outlined as the alleged ringleader of an insurrection linked to his declaration of martial law.

A day earlier, Yoon rejected a request from prosecutors to appear for questioning on Sunday as part of their separate investigation into the martial law declaration.

Yoon reportedly did not comply with the prosecution's summons as he has not completed hiring his legal representatives. Prosecutors plan to demand Yoon to appear before them again on Monday.

If Yoon continues to defy the requests for questioning, prosecutors or the joint investigation team may seek a court-issued arrest warrant for him.

Investigations into the martial law declaration have picked up pace as multiple officials allegedly involved in the incident have been arrested, including former Defense Minister Kim Yong-hyun and the head of the Defense Counterintelligence Command. (Yonhap)