A former South Korean presidential contender accused of raping his female aide has been found not guilty, prompting anger from campaigners.

Ahn Hee-jung’s case is by far the highest-profile in the country’s growing -#MeToo movement. Before the accusations came to light he was widely seen as a strong candidate to replace President Moon Jae-in when his term ends in 2022. He stepped down immediately after he was accused.

On Tuesday, Ahn was acquitted of forced sexual abuse, sexual intercourse by abuse of authority and other charges by the Seoul western district court.

“I am sorry and I am so ashamed,” he said on the courthouse steps. “I have disappointed many. I will make efforts to be born again,” he went on, as women’s rights activists shouted “It’s not over yet!” at him. Prosecutors described the verdict as “incomprehensible” and vowed to appeal.

South Korea remains socially patriarchal despite its economic and technological advances, with a male-dominated legal system often accused of handing out verdicts favouring men in sex abuse cases.

Ahn was governor of South Chungcheong province when his aide Kim Ji-eun told a television interview earlier this year that he had raped her four times after she was hired.

Fighting back tears, she said she had been unable to reject her boss in the rigid hierarchy of her office.

The 53-year-old politician issued a formal apology, stepped down from his post and was later indicted but always insisted the sex was consensual.

The court said it saw “little evidence” that Ahn used his authority to force Kim into sex, adding the evidence presented by the prosecution – which had demanded four years’ jail for Ahn – was “not enough to prove that Kim’s sexual freedom was violated against her will”.

“There are also many things that were questionable and incomprehensible in the victim’s testimony,” the court ruling said.

In a statement read out by her own lawyers, Kim said she would “not feel defeated by today’s unjust result”.

“I will fight … until the day when those using their power to sexually abuse others are held accountable under the laws,” she said.

As the verdict was delivered dozens of women’s rights campaigners condemned Ahn outside the court building, while the politician’s supporters cheered for him.

“Repent, Ahn Hee-jung! What you did was sexual violence!” the activists chanted in unison.

A coalition of dozens of women’s rights groups criticised the verdict for defining the abuse of power at work too narrowly.

“The court failed to recognise the basic reality faced by the victim, in which she had to choose between resisting Ahn’s order or losing her job and livelihood,” they said in a joint statement.

“The verdict will be interpreted as a signal that female aides working for powerful figures in politics, economy or other fields should remain silent even when they are sexually abused.”

The -#MeToo campaign against the abuse of women swept the South this year after Seoul prosecutor Seo Ji-hyeon defied convention to speak out on television about the abuse she suffered at the hands of a powerful superior.

Her move opened the floodgates, prompting more women to come forward to accuse powerful figures in politics, arts, religion, education and entertainment of abuse.

Agence France-Presse