A deadly shooting at the site of a sit-in by Muslim Brotherhood supporters in Cairo, demanding the reinstatement of ousted President Mohamed Morsi, has left dozens of people dead.

The Egyptian health ministry said at least 51 people had been killed and more than 300 injured in the incident early on Monday morning.

Mohamed Mohamed Ibrahim El-Beltagy, a Brotherhood MP, described the incident during dawn prayers after police had stormed the site, as a "massacre".

About 500 people were also reportedly injured.

A doctor told Al Jazeera that "the majority of injured had gunshot wounds to the head".

Speaking to Al Jazeera, Gehad Haddad, a spokesman for Muslim Brotherhood, said that at around 3.30 in the morning, army and police forces started firing at sit-in protesters in front of the Republican Guard headquarters in Cairo.

“We have people hit in the head, we have bullets that exploded as they entered the body, cluttering organs and body parts” said Haddad.

“Every police force in the world understands how to disperse a sit-in. This is just a criminal activity targeting protesters.”

However, the military, which has set up checkpoints around Nasr City, said a "terrorist group" was responsible, adding that two officer had also been killed.

In a press conference held in Cairo on Monday, Hany Abdel Latif, Egypt's interior ministry spokesman, said that "the Egyptian police is the force of the people. They are operating for all the Egyptian people, with all their affiliations."

"The Egyptian security forces are working to safeguard the freedom of the Egyptian people following the January 2011 revolution," said Abdel Latif, adding that the police and security apparatus will not protect any particular regime, not "the former, the existing, or the upcoming".

"The Egyptian police is out of the political equation. It cannot be part of any political process in any way, shape or form," said Abdel Latif.

Calls for an 'uprising'

Egypt's Muslim Brotherhood has called for an "uprising" in the country and asked the "international community to stop the "massacres" in the aftermath of last week's military coup.

The Freedom and Justice Party, the religious group's political arm, demanded "an uprising by the great people of Egypt against those trying to steal their revolution with tanks”.

The party, which had the highest number of seats at the parliament before the coup of last week, urged "the international community and international groups and all the free people of the world to intervene to stop further massacres [...] and prevent a new Syria in the Arab world."

Dozens have died and more than 1,000 people have been injured in street clashes between supporters and opponents of Morsi in the aftermath of the military coup on Wednesday.

The latest violence further raised political tensions, even as the country's interim leadership struggled to find a consensus on who should be the prime minister.

The Salafist Nour Party announced it was suspending its participation from talks over new government in protest against Monday's fatal shootings.

The pro-Morsi camp is refusing to budge until its leader is restored.

PHOTO CAPTION

Supporters of Egypt's President Mohamed Mursi hold pictures of him as they react after the Egyptian army's statement was read out on state TV, at the Raba El-Adwyia mosque square in Cairo July 3, 2013.

Al-Jazeera