South Korean authorities investigating President Yoon Suk-yeol's short-lived declaration of martial law have been calling on him to appear for questioning, amid media reports that Yoon is choosing lawyers to represent him.

Prosecutors issued a summons to Yoon for potential charges of insurrection and abuse of power on Monday. The president also received another one, from a joint investigation unit including police, to appear for questioning at 10 a.m. on Wednesday, local time.

Experts say the police and the prosecutors are running their investigations separately, as if competing with one another. South Korean media outlets reported that Yoon is building his defense team.

Yoon reportedly defied a summons issued by prosecutors on Sunday, citing his need to finish choosing lawyers.

Yoon defended his martial law declaration as an "act of governance" outside the scope of judicial scrutiny, in his address to the public. He said he will steadfastly confront the investigation.

Military commanders involved in Yoon's brief imposition of martial law are also under investigation by prosecutors.