SEOUL - South Korea's senior presidential secretary for political affairs offered Thursday to resign ahead of the expected questioning by prosecutors over a graft scandal involving his former aides.

Jun Byung-hun, senior political affairs secretary for President Moon Jae-in, held a press conference in the presidential office, saying he felt very frustrated to cause troubles to President Moon though he made best efforts to serve the president even for the short period of time.

Jun said he had offered to resign as the senior secretary for the president who was managing state affairs only for people, asking people to protect the Moon government to the end.

He apologized for aberrant acts of his former aides, denying his involvement in any illegal acts.

Prosecutors were expected to summon Jun for questioning in the near future as the prosecution said Wednesday that the questioning would be inevitable. Jun's two former aides were already arrested.