Amnesty International has called on authorities in Iran to “immediately and unconditionally” release a female student who was arrested after stripping to her underwear in what the organisation described as a public protest against harassment relating to the country’s strict dress code.

The incident took place after the woman, who has not been identified, reportedly had a confrontation with members of the Basij paramilitary force who ripped her headscarf and tore at her clothes inside Tehran’s prestigious Islamic Azad University.

Videos posted to social media appear to show the woman removing her clothes and walking out on to the street in her underwear. A second video appears to show the woman being bundled into a car by men in plainclothes.

The student media outlet Amir Kabir newsletter said the woman had been harassed by a Basij member for not wearing a headscarf. Under Iran’s mandatory dress code, women must wear a headscarf and loose-fitting clothes in public.

The media outlet also alleged that she was beaten during the arrest and on Saturday said that information about the woman’s condition and whereabouts was unavailable.

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Amnesty International Iran called for an “independent and impartial” investigation into the allegations of abuse.

“Iran’s authorities must immediately and unconditionally release the university student who was violently arrested after she removed her clothes in protest against abusive enforcement of compulsory veiling by security officials,” it said on social media.

“Pending her release, authorities must protect her from torture and other ill-treatment and ensure access to family and lawyer.”

Iran’s conservative Fars news agency confirmed the incident, saying that the student had worn “inappropriate clothes” and had “stripped” after being told by security guards to comply with the dress code.

In a report that cited “witnesses”, it said that security guards had spoken “calmly” with the student and denied reports that their actions had been aggressive in any way.

The incident comes more than two years after Iran was rocked by nationwide protests after the death in custody of Mahsa Amini, an Iranian Kurdish woman who had been arrested for an alleged breach of the dress code. The protests, during which some women defied authorities to cast off their headscarves, were later violently curbed by authorities.