The family of Mahsa Amini - the 22-year-old whose death in custody sparked protests across Iran - say they are receiving death threats and have been warned not to take part in the demonstrations.
Mahsa was arrested in Tehran last month for not following her country's rules requiring women to wear a hijab. While in custody she was beaten into a coma and declared brain dead by the country's morality police.
Police in Tehran deny she was beaten to death and claimed that during a session of "justification and education", the young woman "suddenly suffered a heart problem".
Speaking to the BBC, her cousin said: "Our family have been under immense pressure from the Islamic Republic's officials, so we don't talk to human rights organisations or channels outside of Iran and inform anyone from the outside world about her passing."
He said that the threats that his family members had received have made them fear for their safety.
"The regime's officials have threatened us through Instagram with fake accounts, and told the family members in Iran that if they get involved in the protests, they might be killed," he said.
"Myself, I have been receiving many threats over the phone, [saying] that if they see me in the city, they will kidnap me and kill me."
An official forensics report claimed Mahsa died from existing medical conditions.
Mahsa’s family insist the young woman was beaten to death by officials who accused her of breaking strict laws requiring women to cover their hair. She was held in capital Tehran on September 13 for “inappropriate attire” and died three days later.
The coroner’s report said her death was “not caused by any blow to the head and limbs”.
Mahsa’s murder has led to three weeks of nationwide unrest as women and girls challenge Iran’s strict religious regime.
Britain said on Monday it had sanctioned senior Iranian security officials and the country's "so-called Morality Police", saying the force had used threats of detention and violence to control what Iranian women wear and how they behave in public.
Citing Mahsa's death and the subsequent protests, Britain said it had sanctioned the morality police in its entirety, as well as both its chief, Mohammed Rostami Cheshmeh Gachi, and the Head of the Tehran Division, Haj Ahmed Mirzaei.
"These sanctions send a clear message to the Iranian authorities - we will hold you to account for your repression of women and girls and for the shocking violence you have inflicted on your own people," Foreign Secretary James Cleverly said in a statement.
