Republic of Korea's President Park Geun-hye personally apologized on Monday for an "unsavory" incident during her US visit that led to the dismissal of her chief spokesman.

Yoon Chang-jung, the spokesman, was sacked over allegations that he had sexually harassed a female intern - an ethnic Korean and US citizen - while accompanying Park on the ROK president's trip, which began on May 5 and ended on Thursday.

"I feel apologetic that an unsavory incident ... occurred near the end of my visit to the US and greatly disappointed the people," Park said at a meeting of senior aides.

"I sincerely apologize for the shock the female student and her parents must have received and the scars left on the hearts of (overseas) compatriots," she said, according to a report of the meeting posted on the presidential Blue House website.

Huh Tae-yeol, presidential chief of staff, also apologized to the victim and her family on Sunday.

"We offer our deepest apology to all South Koreans, the victim, her family and Korean expatriates overseas for the incident," he said, adding he had been left "speechless".

"This is an unacceptable and very shameful incident," he said, without elaborating on its nature.

Huh added that Lee Nam-ki, the top spokesman for Park and Yoon's superior, had offered to resign to take responsibility but did not say whether the resignation had been accepted.

The scandal has dominated media headlines in the ROK for several days, with reports pointing to major discrepancies in the various versions put forward and questioning the Blue House's initial reaction.

Park, the country's first female leader, vowed that all the facts will be investigated so that no "single speck" of suspicion remained.

Washington police have opened an investigation into a complaint filed by the intern over "misdemeanor sexual abuse" by an unnamed 56-year-old male suspect.

A Washington police report obtained by ROK news agency Yonhap and The Washington Post said the intern complained the suspect "grabbed her buttocks without her permission".

Yoon returned to Seoul on Wednesday without accompanying Park on her trip to Los Angeles, the final stop of her US visit. He denied the allegation on Saturday, saying he had merely "patted her waist" in a sign of encouragement.

"I implore her to forgive me if I had hurt her due to differences in culture. I offer my apology to her," he told reporters.

Park said all her officials will cooperate actively with the police investigation.

The affair cast a cloud over Park's US tour - her first overseas trip since taking office in February.

Park met with US President Barack Obama, and the two leaders reaffirmed their united front by offering no concessions in the face of provocations from the Democratic People's Republic of Korea.

She also addressed a joint session of the US Congress, stressing that Pyongyang had to give up its nuclear weapons.

The DPRK was quick to pick up on the Yoon scandal, with the ruling party newspaper Rodong Sinmun saying in a commentary on Sunday that Park's US trip will be remembered for a "shameful" act of indecency.