An Iranian coroner's report into the death of Mahsa Amini said she did not die due to blows to the head and limbs but from multiple organ failure caused by cerebral hypoxia, or lack of oxygen to the brain, the official news agency IRNA reported on Friday.

The death of 22-year-old Amini while in the custody of Iran's morality police has ignited more than two weeks of nationwide protests. Her father has said she suffered bruises to her legs and has held the police responsible for her death.

The coroner's report said her death was "not caused by blow to the head and limbs". It did not say whether she had suffered any injuries.

Amini was arrested in Tehran on Sept 13 for "inappropriate attire", and died three days later while in custody, sparking demonstrations that represent the biggest challenge to Iran's clerical leaders in years.

Referring to the day she collapsed in custody, the coroner's report said she had regained consciousness before falling again due to what it described as underlying diseases.

"Due to the ineffective cardio-respiratory resuscitation in the first critical minutes, she suffered severe hypoxia and as a result brain damage despite recovery from cardiac functioning," it said.

"She died due to multiple organ failure caused by cerebral hypoxia."

The lawyer for Amini's family, Saleh Nikbakht, previously told the semi-official Etemadonline news website that "respectable doctors" believe she was hit in custody.

The police have denied she suffered any harm.

The police had previously said she suffered a heart attack after being taken to a station to be "educated".

Her family deny she had any heart problems.

- Reuters