A man has been found dead at a pro-Morsi sit-in outside Rabaa Al-Adawiya Mosque in Cairo's Nasr City.
The dead man, Amr Kamel, 30, had been tortured, according to his relatives, Al-Ahram Arabic news website reported.
An official forensic report said Kamel's toenails had been removed and he had wounds to the head, chest and back.
He was taken to the nearby Health Insurance Hospital late on Sunday, then moved to the Zeinhom morgue. Ahmed Abdel-Latif of the Egyptian Ambulance Authority was informed of the death by protesters. He then reported the incident to the police.
Kamel's family blame the leaders of the Muslim Brotherhood, who are organising the sit-in, for his death.
They have filed a report with the prosecution to start an investigation.
The streets surrounding Rabaa Al-Adawiya Mosque have been the site of a massive sit-in by supporters of deposed president Mohamed Morsi since 28 June.
The army deposed Morsi on 3 July amid mass nationwide protests against him. His Muslim Brotherhood group has rejected what it says was a military coup against a democratically-elected leader.
