A spokesman for Egypt's Interior Ministry has defended police after 51 members of the Muslim Brotherhood were shot dead in Cairo, saying that history "has vindicated and absolved them of all accusations".

The Islamist group said its members were staging a peaceful sit-in protest in support of ousted president Mohamed Morsi when they were fired on by a combination of police officers and army troops.

However the army said the firing began after a "terrorist group" had tried to storm the barracks.

Police spokesman Hany Abdel Latif said in a press conference that police "protect Egyptian citizens, not the regime" and added that one army and two police officers were killed in the dawn attack by Brotherhood supporters.

Latif's stance was echoed by military spokesman Ahmed Ali who said there were "acts of incitement and provocation to instigate acts of violence from demonstrations against military facilities".

"The armed forces handed down more than one warning that military units and personnel cannot be approached," he said. But the situation spiralled out of control at around 4am, when an armed group attacked the area around the Republican Guard HQ.

Stones, bombs and molotov cocktails

Ali claimed that the security personnel attacked with live ammunition, adding: "at the same time other groups started to climb up the buildings nearby and throw stones, molotov cocktails, bombs and heavy objects."

Ali claimed the army officer died during this assault, when he was shot through the top of the head from above - indicating that snipers were firing from high buildings. The spokesman assured reporters he was going to hand out a video clip showing the real version of events which allegedly shows protesters on roofs, throwing objects to the law enforcement officials.

"We are heading towards a truly democratic civil state," Ali said. "The last few days have made us more proud of being Egyptian. The new Egypt cannot be built by one particular party or sect."

The office of interim president Adly Mansour expressed "deep sorrow" over the deaths and called for restraint. However tension continues to run high within both pro and anti-Morsi groups.

The Brotherhood's political wing, the Freedom and Justice Party (FJP) has rejected the official version of events and called on Egyptians to stage an "uprising" against "those trying to steal their revolution with tanks". The party warned that Egypt could become the new Syria and called for the international community to "stop further massacres".

The hardline Salafist Nour Party said it was pulling out from talks to choose an interim prime minister, citing the Republican Guards HQ's incident as a "massacre".

Meanwhile the crackdown on Al Jazeera, the pan-Arab broadcast network perceived as favouring Morsi, continues. Before the police news conference, reporters for the network were kicked out by Egyptian journalists chanting "Al-Jazeera out".