SEOUL (Reuters) - South Korea's Olympic swimming champion Park Tae-hwan choked back tears on Friday as he apologised for a failed doping test that led to an 18-month ban from the sport.

He said he wished he could turn back time and do things differently.

Swimming's governing body Fina handed out the ban on Monday at a hearing in Switzerland after the 25-year-old had tested positive for testosterone ahead of the Asian Games in September.

Park, one of South Korea's most popular athletes, tested positive after he was given a shot at a clinic.

"The last few months since the doping results came out have been hell," he told reporters at a Seoul hotel.

"When I first heard that I had tested positive, I thought for sure it must be some mistake. I thought: Why did this happen to me? What if I didn't go to that hospital? What if I didn't let the doctor inject me? If I could only go back in time."

He added that he had gone to the clinic seeking treatment for a skin complaint and, after being prescribed vitamins, he had explained to the doctor that he could not take anything that might be on the banned substances list.

The hospital had assured him he was receiving only vitamins, he added.

South Korea's Yonhap news agency has reported that Seoul prosecutors have charged a doctor with professional negligence and the trial is set to begin next month.