The National Alliance to Support Legitimacy has called on "all Egyptian people" to take to the streets "to stop the massacre" after police attacked its two sit-ins in Cairo’s Nahda and Rabaa El-Adaweya squares early on Wednesday.
The alliance, an Islamist group led by the Muslim Brotherhood in support of ousted president Mohamed Morsi, asked their supporters to head to the sites of the sit-ins.
They determined a number of gathering points including El-Istiqama Mosque in Giza, El-Fath Mosque in downtown Ramses, El-Nour Mosque in Abbassiya, Assad El-Furat Mosque in Dokki and Al-Alf Maskan Mosque near Heliopolis district.
Shortly after dawn on Wednesday, police dispersed a sit-in near the Giza zoo and started clearing out another encampment at Rabaa El-Adaweya mosque in northern Cairo.
Conflicting reports emerged on the casualties. The Brotherhood claimed 120 were killed while the health ministry put the death toll at five and said at least 52 were injured.
The interior ministry said that a policeman and a conscript were killed and nine injured.
Pro-Morsi protests have already started to spread. Protesters have partially closed off the main Gameat El-Dowal El-Arabiya street in Giza's Mohandeseen district, sparking clashes with police forces who attempted to disperse the demonstration.
In Egypt's second city of Alexandria, state news agency MENA reported that a number of pro-Morsi supporters blocked the main corniche road in response to the attacks on Cairo’s sit-ins.
Meanwhile, vice-chairman of the Brotherhood's Freedom and Justice Party Essam El-Erian condemned the attacks, saying Morsi supporters will remain defiant.
"Hundreds of martyrs will fall and our determination will never be broken ... So we shall live freely in a free country," he said.
Brotherhood spokesman Gehad El-Hadad wrote on Twitter, "You will not bend our will or break our resolve with your audacity to kill. We will always stand high in face of any tyranny."
The Brotherhood holds Defence Minister Abdel Fattah El-Sisi and interior minister Mohamed Ibrahim "fully responsible of every blood drop and any life lost," the group’s spokesman Ahmed Aref said.
Morsi was ousted on 3 July by the army amid mass nationwide protests against him. Around 300 have been killed in clashes pitting his supporters against opponents and security forces since then.