Friday's raid was carried out through a process in which the prosecution submitted to the presidential office a court-issued search warrant and a list of documents it planned to obtain.

Investigators were reportedly focusing on finding links between the presidential unit and Song's campaign pledge to build a public hospital in Ulsan on suspicions that some officials helped design the mayor's election pledges.

The election-meddling allegations triggered a massive investigation after former mayor Kim claimed that the Ulsan Metropolitan Police Agency deliberately raided his office a few months ahead of the election and that the presidential office was behind the move.

Kim alleged that some presidential officials compiled a document on bribery allegations involving his confidants based on tips from the city's Vice Mayor Song Byung-gi, which led to the raid that negatively affected his election campaign.

The raid marks the second search of Cheong Wa Dae in a month.

In December, prosecutors searched the presidential office in connection with another probe into an alleged cover-up of an inspection into an ex-vice mayor who faces bribery charges.

Prosecutors were seeking to secure evidence on why a special inspection into the former Busan vice mayor was abruptly suspended, leading him to avoid punishment for an unknown reason and become the port city's vice mayor in 2018. (Yonhap)