Prosecutors began to question Jun Byung-hun, former senior presidential secretary for political affairs, on Monday morning as a suspect in a bribery case involving his two former aides.

The 59-year-old veteran politician appeared at the Seoul Central District Prosecutors' Office at around 10 a.m. He stepped down over the scandal Thursday.

"I say this again. I have never been involved in anything illegal. I will explain myself to the prosecution over the suspicion and misunderstanding," he told reporters. "I apologize for my two former aides' lapses. ... I feel terrible that I brought trouble to (the presidential office)."

His two former aides were arrested on bribery charges on Nov. 10. In 2015 they allegedly pressured a local home shopping channel to donate 330 million ($301,150) to the Korea e-Sports Association, which had ties with Jun.

The cable channel, Lotte Homeshopping, is suspected of giving the money to seek Jun's influence for the renewal of its broadcasting license. Jun, then a lawmaker, belonged to the parliamentary committee in charge of media policies. He was also the e-sports association's honorary chairman at the time.

Jun is the first high-profile official in the Moon Jae-in government to face a corruption probe. He has denied any wrongdoing.

Prosecutors are known to have secured statements from the home shopping channel's officials saying they were considering his influence when they decided to donate.

Prosecutors also apparently have financial records that show that Jun's family made transactions with Lotte vouchers.

Prosecutors are said to be considering filing an arrest warrant for Jun pending further investigation. (Yonhap)