Prosecutors on Sunday questioned a former deputy director of the National Intelligence Service (NIS) allegedly involved in the spy agency's illegal surveillance of officials and civilians.

Choi Yun-su, who was in charge of information gathering of domestic affairs between February 2016 and June 2017, appeared at the Seoul Central District Court in the morning.

He was the supervisor of Choo Myeong-ho, who was arrested on Nov. 3 for illegally spying on public servants, activists and celebrities deemed critical of the conservative government of then-President Park Geun-hye, who was ousted in March for corruption.

Choo allegedly reported his team's secretive operations to Woo Byeong-woo, then presidential secretary for civil affairs.

Choi, a former senior prosecutor, is suspected of involvement of surveillance activities, including their monitoring of a special investigator who was probing Woo over allegations of abuse of power.

The prosecution plans to summon Woo soon.

It is part of a series of probes into alleged government misdeeds of the past conservative administrations, which the opposition parties label "political retribution." (Yonhap)