The chief of the prosecution office on South Korea's southern island of Jeju resigned on Monday over allegations that he committed a lewd act on the street, the justice ministry said.

Kim Soo-chang, the 52-year-old chief of Jeju District Prosecutors' Office, has faced a police probe since last week after he allegedly masturbated in public near his residence on the resort island.

After being detained at the scene at around midnight on Wednesday upon a report by a teenage witness, Kim refused to identify himself and denied the allegations during questioning, according to police.

He was sent home the next day, with investigators yet to determine what charges to bring against him.

"Kim offered to step down from the post earlier in the day, and we accepted the offer," the ministry said.

"Although the case has nothing to do with his duty, it is inappropriate for him to take charge of legal cases while under investigation," the ministry said. "Accepting the offer is intended to boost the fairness and credibility of the ongoing investigation."

The Jeju Provincial Police Agency said it has asked the National Institute for Scientific Investigation "to analyze footage from three closed-circuit television cameras near the scene. The results are due later this week."

Citing the sensitivity of the case, the police said they will announce details after the results of the analysis become available.

Pleading his innocence and claiming that he was mistaken for someone else, Kim had taken five days off from work from Monday, according to a prosecutor at the Jeju office. 

As a career prosecutor of nearly 25 years, Kim took office as the Jeju office's chief last year. (Yonhap)