The state anti-corruption investigation office has checked the phone logs of 60 lawmakers of the main opposition People Power Party (PPP), the party said Wednesday, accusing the powerful investigative agency of illegal surveillance.

The Corruption Investigation Office for High-ranking Officials (CIO) has come under fire following revelations that it obtained the phone records of journalists, politicians and their family members in an alleged attempt to identify the source of leaks to the media.

The PPP said it has found that an additional 21 lawmakers were subject to the surveillance. The party, which has 105 lawmakers in the 295-member National Assembly, had said Monday that 39 lawmakers had their phone records checked.

Floor leader Rep. Kim Gi-hyeon and chief policymaker Rep. Kim Do-eup were among those whose phone logs were checked. Six aides to lawmakers were also on the list.

The PPP has demanded the CIO's chief step down, and called for the office's abolition.

PPP presidential nominee Yoon Suk-yeol wrote on Facebook that if elected, he will demand accountability from those responsible for the CIO's "illegal actions."

"The reasons we need a change of government through the upcoming presidential election are growing one by one," he wrote.

"The biggest reason is the CIO."

The CIO was launched in January as part of the Moon Jae-in administration's drive to reform the prosecution. The office is tasked with investigating corruption among senior public officials and their families. (Yonhap)