Investigations into the circumstances surrounding South Korean President Yoon Suk-yeol's declaration of martial law earlier this month appear to be making progress as authorities question his aides in the military.

South Korean media have reported that according to the chief of the military's counterintelligence command, who himself is under investigation, Yoon had already planned to implement martial law by early November.

Multiple South Korean news organizations say the officer told investigators he heard that Yoon had indicated his intention to declare martial law in early November and conveyed this to former Defense Minister Kim Yong-hyun.

The officer reportedly said Yoon discussed with Kim the possibility of declaring martial law and not attending the summit of the Asia-Pacific Economic Cooperation forum held in Peru mid-November.

Yoon ultimately opted to attend the APEC talks.

Speculation is growing that the officer's statements will have an impact on the ongoing investigation into Yoon.