At least 76 protesters have been killed by Iranian security forces during 11 days of unrest sparked by the death of a woman in custody, activists say.
Iran Human Rights (IHR), a Norway-based organisation, accused authorities of using disproportionate force and live ammunition to suppress the dissent.
Hundreds of people have also been arrested, 20 of them journalists
"The risk of torture and ill-treatment of protesters is serious and the use of live ammunition against protesters is an international crime," said IHR's director Mahmood Amiry-Moghaddam. "The world must defend the Iranian people's demands for their fundamental rights."
The anti-government demonstrations have spread to more than 80 cities and towns across Iran since the funeral of Mahsa Amini on 17 September.
The 22-year-old Kurdish woman from the north-western city of Saqez had been visiting the capital, Tehran, on 13 September when she was arrested by morality police officers for allegedly violating the strict law requiring women to cover their hair with a hijab, or headscarf.
She collapsed after being taken to a detention centre to be "educated" and died in hospital following three days in a coma.