SEOUL -- South Korea's impeached President Yoon Suk-yeol on Wednesday defied the second summons by a joint investigation unit for questioning over the imposition of an emergency martial law, Yonhap news agency reported.

The unit, composed of the police, the defense ministry's investigation headquarters and the Corruption Investigation Office for High-ranking Officials (CIO), sent its second summons to Yoon last Friday, requesting him to appear for questioning by 10:00 a.m. local time on Wednesday as part of its investigation into his short-lived imposition of the martial law on Dec. 3.

The embattled president did not comply with the CIO's first summons last week.

The CIO was currently planning to wait for Yoon's possible appearance later in the day, Yonhap said.

The corruption investigative body said it will make a decision as early as Thursday on whether to send summons for the third time if Yoon refuses to show up for questioning on Wednesday, Yonhap added.

Yoon was named by investigative agencies as a suspect on a rebellion charge following the martial law imposition that was revoked by the National Assembly hours later.