Armita Geravand, 16, suffered "severe injuries" at the hands of the so-called morality police at Shohada Station in Tehran at the start of October, human rights organisation Hengaw said.

Hengaw claimed Armita was dragged out of a train and shared an image it says shows her in a bed at Fajr Hospital.

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In an update on Sunday, the Islamic Republic of Iran News Network said: "Follow-ups on the latest health condition of Armita Geravand indicate that her health condition as brain dead seems certain despite the efforts of the medical staff."

The case raised concerns the teenager could suffer the same fate as Mahsa Amini, the 22-year-old woman whose death last year while in the custody of morality police prompted nationwide protests.

One activist said security forces had forbidden her parents from posting her picture on social media, or talking to human rights groups.

In a video, shared by the state news agency, IRNA, Armita's parents said their daughter had suffered a drop in blood pressure and lost her balance, hitting her head.

Human rights groups have claimed her parent's statement was made under duress. They are asking for footage from inside the train to be published.

But footage shared with IRNA appeared to show Armita walking towards the train with two female friends. After boarding, one of the girls is dragged out by passengers.

Sky News has not been able to independently verify the footage.

Masoud Dorosti, head of the Tehran Metro Operating Company, said the CCTV footage shows no sign of conflict.

The interior ministry of Iran has not immediately replied to requests for comment.