This photo shows the entrance of the Corruption Investigation Office for High-ranking Officials in Gwacheon, Gyeonggi Province, Jan. 19. Yonhap

A state anti-corruption investigation agency probing impeached President Yoon Suk Yeol's martial law case on Sunday requested that he appear for questioning later in the day, hours after a court approved his formal arrest.

The Corruption Investigation Office for High-ranking Officials (CIO) said it has requested Yoon to appear for questioning at 2 p.m.

Yoon was formally arrested earlier in the day after the Seoul Western District Court granted the arrest warrant requested by the CIO.

The CIO, which had faced challenges in investigating the defiant president, expressed "deep regret" that Yoon "appears to deny the rule of law" without any effort to "resolve the issue within the judicial system."

"If he can't accept the warrant issuance, he could follow the appeal or remedy process to overturn it within the judicial system," it added.

The agency also noted the need for safety measures for investigators, as protesters stormed the court in protest against the warrant issuance, threatening police and law enforcement officers. (Yonhap)