A high-profile Chinese activist in the UK who was inundated with deepfake posts on X portraying her as a sexually promiscuous drug addict was told that the abuse did not breach the rules of Elon Musk’s platform.

Apple Peiqing Ni, the 27-year-old founder of the UK-based China Dissent Network, had been advised by UK police to complain to the US-headquartered platform after she was targeted by what she believes is a pro-regime bot.

The abuse included 12 posts tagging Ni and containing fake photographs and videos of her. The captions variously described her as having “chronically chaotic sexual relationships” and being a heavy drug user.

One post also incorrectly said – and celebrated – that Ni had been “beaten badly on the red streets of London while protesting with other anti-China groups”. It went on: “This humiliating defeat is the perfect retribution for her extreme behaviour.”

That claim appeared to be a reference to an attack by masked men on a male activist last March at a sit-in on Trafalgar Square organised by Ni.

The posts on X followed Ni posting that she would be joining a commemoration of the Tiananmen massacre on 4 June in Sutton, south London.

In response to Ni’s complaints, X’s automated systems said the posts did not breach the platform’s rules on harassment or violent speech. A follow-up complaint to the platform’s support service was also rejected.

This was despite X’s rules prohibiting “the malicious, unreciprocated targeting (such as mentioning or tagging) of individual(s), particularly when shared to humiliate or degrade someone”.

The account was only suspended hours after the Guardian raised the decisions on the complaints with X’s press office and sought an explanation. Ni was subsequently informed that X had acted in response to “different reports” regarding the content.

The saga raises questions over X’s internal systems. Ni, who moved to the UK in 2019 to study, said she could not understand why X had not immediately acted to protect her from the abuse.

She said: “I posted a poster for the Tiananmen Square massacre commemoration in Sutton and right after that, that account made deepfake images about me. They’ve been tagging my username since they started it.

“I called the police; they did visit me, but they said because X is an American company and they cannot identify the individual behind the account, they cannot do anything about it. They advised me to report, which I did. And I asked many of my friends and members to do it.”

Ni recently set up the China Dissent Network, an organisation that aims to create a safe space for Chinese dissidents. She is also working with the group UK-China Transparency on a free speech campaign for Hong Kong and Chinese students on UK campuses.

Ni claimed that her parents had been contacted by the secret police in China over her activism in the UK. “My parents are being harassed in China, saying their business will be influenced, and my grandpa’s grave will be dug out if I continue my activism overseas,” she said. “They’ve visited my parents few times.”

Ni said that one of the posts accusing her of animal abuse had correctly written that she had a cat. She said: “I feel like they’re doing some kind of profiling of me … Every time I go out, I feel like I might be followed or watched. And I actually think that might be the case.”

Concerns about antisemitic and anti-Muslim material on X led to an announcement last month of an agreement between the UK regulator Ofcom and the platform over “illegal hate and terror content”.

X agreed to review and assess UK suspected illegal terrorist and hate content on average within 24 hours of it being reported, but Ni said there appeared to be a lack of interest in cracking down on harassment faced by Chinese dissident voices.

X did not respond to a request for comment.