An Iranian doctor who treated victims of torture at Tehran's most feared prison has died, amid conflicting reports of a heart attack, a car accident or suicide — raising opposition accusations that the 26-year-old was killed.

Revelations that protesters detained in Iran's postelection crackdown were tortured, some to death, were a deep embarrassment to the country's clerical rulers. Dr. Ramin Pourandarjani was pressured to change the death certificate of one of the most well known victims and later spoke to a parliament commission investigating the abuse, opposition Web sites reported.

Much of the abuse took place at a facility known as Kahrizak on Tehran's outskirts, where Pourandarjani — a general practitioner — was the only doctor, serving there once a week as part of his mandatory military service.