Protesters said they will not back down from their demands that Morsi, who was removed from power by Egypt's army on July 3, is reinstated, the BBC reported.
"Regardless of what happens to the president, we will continue our protest. Our numbers are increasing every day. Citizens are recognizing the tyranny and the long-term danger of the military coup," said Gehad el-Haddad, a spokesman for the pro-Morsi Muslim Brotherhood. "It may take weeks, months, more than a year -- we will still hold our ground."
The protesters' defied orders to move from their position at the Rabaa al-Adawiya mosque in Cairo, despite threats from government officials, the BBC said.
Interior Minister Mohammed Ibrahim told the supporters to "come to their senses" and go home or they would "soon" be dispersed.
In a televised address Saturday, Ibrahim accused the Brotherhood of deliberately causing a crisis. He denied police had opened fire on the protesters, the website said.
The National Salvation Front in Egypt called on the army to respect human rights and end the bloodshed which has claimed dozens of lives.
The party demanded an independent judicial commission to investigate the violence Friday and Saturday in which some 120 protesters were killed and 4,500 injured, Ahram Online reported Sunday.
"Based on reports of the committee, all those responsible must be held accountable, including the minister of interior, if it is proven that the security forces were involved in excessive use of force against protesters," an NSF statement said.
The Muslim Brotherhood claimed that police used live ammunition to disperse the crowd, however, Interior ministry spokesman HaniAbdel-Latif denied that police used live ammunition, saying they only used teargas.
Egyptian Vice President Mohamed El-Baradei Saturday condemned the alleged "excessive use of force" on Twitter, Ahram Online reported.
"I am working hard and in every direction to end the confrontation peacefully," he said.
Meanwhile, Egypt's "Rebel" campaign issued a statement expressed concern over the Interior Ministry's plan to strengthen security measures in the name of fighting terrorism, Ahram Online said.
"Our campaign supports the state's plans in fighting terrorism, however, we have earlier stressed that this support doesn't include the taking of extraordinary measures, or the contradiction of freedoms and human rights," said Mahmoud Badr, spokesman of the Rebel campaign, in a press statement, adding, "We will never accept the return of Mubarak's state security [apparatus] or the chasing of political activists under any name."
Renewed violence was reported in Port Said Sunday, where 15 Muslim Brotherhood supporters were injured in clashes with security forces during a funeral, the Middle East News Agency said.