An anti-corruption agency raided the presidential office on Wednesday as part of an investigation into an aide's alleged involvement in a controversial travel ban on a former vice justice minister. 

Investigators from the Corruption Investigation Office for High-ranking Officials(CIO) searched the office of presidential civil affairs secretary Lee Gwang-cheol for nine hours from 10 a.m. 

The officers conducted the search by requesting that the top office voluntarily submit documents related to Lee's charges. 

The CIO raided Lee's home the previous day and secured materials related to the probe, and attempted to raid his office as well, but were unable to do so as he did not come to work.

Current regulations state that investigators must receive approval from ranking officials before conducting raids at top-security locations such as the presidential Blue House.

Lee is accused of colluding with the chief of the Korea Immigration Service and prosecutor Lee Kyu-won to use falsified documents to prevent former Vice Justice Minister Kim Hak-ui from leaving the country.

The CIO took over the case in March from the Seoul Central District Prosecutors' Office and has questioned prosecutor Lee three times.