JK Rowling has returned a human rights award given to her by the family of Robert Kennedy after they denounced her stance on women’s rights as transphobic.

The author of the Harry Potter books gave back the award, which she was given at a lavish ceremony in New York in December, after she was criticised by Kerry Kennedy, the late senator’s daughter and president of the humanitarian organisation set up in his name.

Ms Kennedy, 60, wrote on the organisation’s website earlier this month that she had spoken to the author “to express my profound disappointment that she has chosen to use her remarkable gifts to create a narrative that diminishes the identity of trans and non-binary people”.

She added that the transgender community “disproportionately suffers from violence, discrimination, harassment, and exclusion” leading to suicide and mental and bodily harm. “From her own words, I take Rowling’s position to be that the sex one is assigned at birth is the primary and determinative factor of one’s gender, regardless of one’s gender identity — a position that I categorically reject.”

Rowling, 55, began a debate over trans rights in June when she tweeted her dissatisfaction with a headline in an article on an international development website in which the phrase “people who menstruate” was used instead of “women”.

After a backlash on Twitter she elaborated her views in a 3,700-word article on her website, where she described her empathy with trans women but criticised attempts to “erode ‘woman’ as a political and biological class”.

Rowling posted a 620-word statement today rebutting Ms Kennedy’s denunciation.

“The statement incorrectly implied that I was transphobic, and that I am responsible for harm to trans people,” Rowling wrote. “As a longstanding donor to LGBT charities and a supporter of trans people’s right to live free of persecution, I absolutely refute the accusation that I hate trans people or wish them ill, or that standing up for the rights of women is wrong, discriminatory, or incites harm or violence to the trans community.”

She said that she had been overwhelmed by thousands of private emails of support of her views, many of whom felt “vulnerable and afraid because of the toxicity surrounding this discussion”.

Rowling said that she felt “nothing but sympathy towards those with gender dysphoria” and urged investigation of the causes, but was concerned about vulnerable girls being encouraged to undergo lifelong medical treatment.

“[Clinicians and therapists] along with a growing number of other experts and whistleblowers are critical of the ‘affirmative’ model being widely adopted, and are also concerned about the huge rise in the numbers of girls wanting to transition.”

She said that she had been contacted by women who believe that they were wrongly encouraged to undergo transition.

“I’ve been forced to the unhappy conclusion that an ethical and medical scandal is brewing. I believe the time is coming when those organisations and individuals who have uncritically embraced fashionable dogma, and demonised those urging caution, will have to answer for the harm they’ve enabled.”

She said that she had returned the Ripple of Hope award, which she received at a ceremony alongside the American politician Nancy Pelosi. She was recognised for her foundation of Lumos, an organisation dedicated to finding families for children in orphanages.

Since she entered the debate, Rowling has been opposed by all of the actors who performed the principal roles in the Harry Potter films and has been attacked by fan sites devoted to her books.

Rowling concluded: “No award or honour, no matter my admiration for the person for whom it was named, means so much to me that I would forfeit the right to follow the dictates of my own conscience.”