Huh Tae-yeol, the chief of staff, said the case was "unconditionally wrong," "very shameful" and "unacceptable by common sense," Yonhap News Agency reported.
Former presidential spokesman Yoon Chang-jung is accused of sexually assaulting a 21-year-old Korean-American hired as his temporary secretary at a hotel in Washington, D.C., on Tuesday while he was accompanying President Park Geun-hye on her first official trip to the United States. A U.S. police report stated the alleged victim said Yoon "grabbed her buttocks without her permission."
He returned to Seoul Wednesday and has since been questioned by police about the incident. He has denied the allegations.
Other senior presidential officials have also apologized for the incident.
"I am so apologetic and sorry that the embarrassing and unsavory incident involving a senior Cheong Wa Dae official deeply hurt the hearts of the people. This is unconditionally wrong so much so that I would have no words to offer even if I had 10 mouths," said Lee Nam-ki, a senior press secretary.
Lee has offered to resign after returning to Seoul from the United States this week with Park. There has been no word as to whether his resignation has been accepted.
"Apart from law, this case is a very shameful incident unacceptable by common sense," he said.