SEOUL -- South Korea's joint investigation unit sent its second summons Friday to impeached President Yoon Suk-yeol, according to Yonhap news agency.

The unit, composed of the police, the defense ministry's investigation headquarters and the Corruption Investigation Office for High-ranking Officials (CIO), called on Yoon to appear for questioning on Dec. 25 over insurrection charge.

The summons were sent by express and electronic mails to the presidential residence and the presidential office.

The CIO attempted to deliver its first summons to the embattled president last week, but it failed as the presidential security service refused to receive it.

The prosecution separately sent its second summons to ask Yoon to appear for questioning on Saturday, but it was actually invalid after the prosecution transferred the case to the CIO earlier this week.

The CIO reportedly planned to consider seeking an arrest warrant against Yoon if Yoon continues to avoid receiving the summons or fails to comply with the summons for no justifiable reasons.

Yoon was named by investigative agencies as a suspect on rebellion charge following his martial law imposition on the night of Dec. 3 that was revoked by the National Assembly hours later.

The impeachment motion against Yoon was passed by the National Assembly on Dec. 14 and delivered to the constitutional court to deliberate it for up to 180 days, during which Yoon's presidential power is suspended.