They have seen dozens killed among their ranks and their prospects of success appear remote but supporters of Egypt's deposed president Mohamed Morsi have faith he will be reinstated.

"Together in support of legitimacy," a giant banner proclaims at the entrance to their Cairo tent camp, adorned with pictures of Morsi, who has not been seen in public since the military removed him on July 3.

Three rings of Islamist volunteers guard access to the camp around Rabaa al-Adawiya mosque in the Nasr City suburb of northeast Cairo, where many women figure among Morsi loyalists who have been camped out for weeks.

"We are prepared to die," said Khaled Khalil, a bearded and smiling sociology professor, shielding himself from the sun under a carton poster of Morsi.

He said former president Hosni Mubarak who was ousted in a 2011 uprising "fell in a peaceful way" and that, "God willing, Sisi will fall in the same peaceful way," referring to army chief General Abdel Fattah al-Sisi who led the coup that deposed Morsi after widespread protests against the Islamists.

Behind him, a small group of men pushed a wheelbarrow filled with sand to reinforce makeshift barricades around the camp, which Egypt's interim authorities have vowed to dismantle soon, using force if needed.

"Our only arms are our prayer rugs and the Koran (holy book). The other camp has bullets and gas," said Dhahi Abdallah, a Morsi supporter from the Nile Delta, north of the Egyptian capital.

On Saturday in Cairo, 72 people were killed during clashes near Rabaa al-Adawiya mosque between demonstrators and security forces, according to health ministry figures.

Morsi portraits and lists of "martyrs" from his Muslim Brotherhood have been posted around the outskirts of the mosque, featuring their names and home regions.

"The Lord is with us. He who has right and legitimacy on his side fears no one," said Brotherhood activist Ali Shafiq. "Either we live in dignity on our land and in our country, or we die with honour."

The young man, from the same province as Morsi, maintained that protesters had been "peaceful in the face of the bullets, tanks and armoured cars" of the military.

Security forces, meanwhile, have deployed reinforcements and armoured cars around the mosque area, while Morsi supporters have erected brick barricades on neighbouring roads.

Morsi supporters have accused security forces of using live fire against unarmed protesters, but the interior ministry insisted its forces had only fired tear gas.

Interior Minister Mohammed Ibrahim has called on protesters to "come to their senses" and go home.

The violence, the worst since Morsi's ouster, prompted international condemnation, with Human Rights Watch accusing Egyptian authorities of "criminal disregard for people's lives."

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