Female protesters have been at the forefront of escalating protests in Iran and have been burning headscarves, after the death in custody of a woman detained for breaking hijab laws.
Demonstrations have continued for five successive nights, and reached several towns and cities.
Mahsa Amini died in hospital on Friday after spending three days in a coma.
In Sari, north of Tehran, large crowds cheered as women set their hijabs alight in defiant acts of protest.
Ms Amini was arrested in the capital last week by Iran’s morality police, accused of breaking the law requiring women to cover their hair with a hijab, or headscarf, and their arms and legs with loose clothing.
She fell into a coma shortly after collapsing at a detention centre.
There were reports that police beat Ms Amini’s head with a baton and banged her head against one of their vehicles, Acting UN High Commissioner for Human Rights Nada al-Nashif said.
The police have denied that she was mistreated and said she suffered “sudden heart failure”. Ms Amini’s family has said she was fit and healthy.
“Mahsa Amini’s tragic death and allegations of torture and ill-treatment must be promptly, impartially and effectively investigated by an independent competent authority, that ensures, in particular, that her family has access to justice and truth,” Ms Nashif said.
She noted that the UN had received “numerous, and verified, videos of violent treatment of women” as morality police expanded their street patrols in recent months to crack down on those perceived to be wearing “loose hijab”.
“The authorities must stop targeting, harassing, and detaining women who do not abide by the hijab rules,” she added, calling for their repeal.
An aide to Iran’s Supreme Leader Ayatollah Ali Khamenei paid a visit to Ms Amini’s family on Monday and told them that “all institutions will take action to defend the rights that were violated”, state media reported.
Senior MP Jalal Rashidi Koochi publicly criticised the morality police, saying the force was a “mistake” as it had only produced “loss and damage” for Iran.
The 22-year-old was from Kurdistan Province in western Iran, where three people were killed on Monday as security forces opened fire on protesters. [BBC NEWS]