The Muslim Brotherhood called on Egyptians to rise up against those who "want to steal" the revolution, a statement by its political wing said on Monday. Some 51 people were killed in shooting outside the Cairo headquarters of the Republican Guard, according to state media, where it is believed that ousted President Mohammed Morsi is being held.
Egyptian state media also reported that an additional 430 people were wounded.
After the shooting, the Muslim Brotherhood said that the chief of the armed forces, General Abel Fattah al-Sisi wanted to drive Egypt to the same fate as Syria. Holding him responsible, the group described the shooting as a "horrible crime" in a statement posted on Facebook.
"(The Freedom and Justice Party) calls on the great Egyptian people to rise up against those who want to steal their revolution with tanks and armored vehicles, even over the dead bodies of the people," a statement on the party's Facebook page said.
The bloodshed deepened Egypt's political crisis, escalating the struggle between the army, which overthrew Islamist President Mohammed Morsi last Wednesday after mass demonstrations demanding his resignation, and the Brotherhood, which has denounced what it called a coup.
The Egyptian military said "a terrorist group" had tried to storm the building in the early hourse of Monday. The bloodshed Monday in Cairo also left two policemen and one soldier dead.
An Egyptian military official who declined to be named because he was not authorized to brief reporters, said a group had tried to storm the headquarters of the Republican Guard. He added that those killed had been Morsi supporters camped outside the building in protest at his overthrow.
Murad Ali of the Brotherhood's Freedom and Justice Party said shooting broke out in the early morning while Islamists staged a sit-in outside the Republican Guard barracks. The Brotherhood's official spokesman, Gehad El-Haddad, who is at a pro-Morsi sit-in at a mosque near the scene, said 37 Morsi supporters had been killed.
Al Jazeera's Egypt news channel broadcast footage of what appeared to be five men killed in the violence, and medics applying cardiopulmonary resuscitation to an unconscious man at a makeshift clinic at a nearby pro-Morsi sit-in.
Ambulances were shown driving to and from the clinic.
The military overthrew Morsi last Wednesday after mass nationwide demonstrations led by youth activists demanding his resignation. The Brotherhood denounced the intervention as a coup and vowed peaceful resistance against the "usurper authorities."
The ultraconservative Islamist Nour party, which backed the military action, said it had withdrawn from negotiations to form a new interim government in protest at what it called the "massacre of the Republican Guard."
"We've announced our withdrawal from all tracks of negotiations as a first response," Nader Bakar, spokesman for Egypt's second biggest Islamist party, said on Facebook.
Turkish Foreign Minister Ahmet Davutoglu condemned the Cairo shooting, describing the incident as a "massacre" and calling for the start of a normalization process.
"I strongly condemn the massacre that took place in Egypt at morning prayer in the name of the fundamental human values which we have been advocating," Davutoglu said on Twitter.
Davutoglu last week denounced the Egyptian army's removal of Morsi after days of mass unrest against his rule "a military coup" and said this was "unacceptable."
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