Former President Yoon Suk Yeol's detention is again up in the air as his treason trial begins.

The Seoul Central District Court’s Criminal Division 36 held the first preparatory hearing of the case on Monday, though the defendant's presence was not required.

The court scheduled a December 23 hearing at 2:30 p.m. to review the special counsel’s request for renewed detention, with Yoon’s current detention order set to expire on January 18.

A court ordered Yoon's release from custody in March, but he was jailed again in July in connection with the martial law investigation.

Large portions of the upcoming proceedings are expected to be closed to the public, with the court citing risks of state secrets leaking during argument and evidence review.

Prosecutors allege that Yoon ordered the Drone Operations Command to send an unmanned aircraft toward Pyongyang in October last year to justify his declaration of martial law, a charge he faces alongside former Defense Minister Kim Yong-hyun and former military intelligence chief Yeo In-hyung.