Prosecutors have begun on Monday afternoon an investigation into the bloody clashes between the Egyptian army and pro-Morsi protesters at the Republican Guard headquarters in Cairo earlier in the day.
The clashes left at least 51 civilians dead and 435 injured, the ministry of health said on Monday afternoon.
Meanwhile, the Egyptian army said one officer died and 42 soldiers were injured, including eight in critical condition.
Prosecutors said they had found bullets, birdshot and Molotov cocktails in the vicinity of the clashes near the Republican Guard headquarters in Cairo's Nasr City.
A delegation of prosecutors visited Zenhom morgue where some of the dead were taken, while another interviewed victims in local hospitals.
A number of mourners showed Ahram Online the forensic reports of those killed, most detailed that they died from gunshot wounds to the back and shoulders, with exit wounds to the chest and abdomen. Those gathered outside the morgue maintained that this is proof the deceased had their backs to the army when gunned down: again impossible to independently verify.
"I was in Rabaa Al-Adawiya sit in by the mosque, by brother Ahmed was by Salam Salem sit-in when the attack happened," says Mohamed Ismail, 43, who had come to pick up his brother's body, "He was shot in his back and chest, it says many of his internal organs were damaged."
Another man Mohamed Khatiba outside the morgue was carrying the blood-stained bag 21-year-old student Ahmed Hamid Mohamed Hahim had with him when he was shot. He says his relative received wounds to his chest, stomach and legs.
Doctors at the morgue, who had been working in the field, told Ahram Online they had over 50 dead, and the majority of those died from bullet wounds or asphyxiation due to tear gas.
Conflicting reports have emerged on how the clashes started on the fifth day of a Muslim Brotherhood spearheaded sit-in at the army facility to demand the return of deposed President Mohamed Morsi.
In an official statement published by Al-Ahram Arabic news website, the army said an "armed terrorist group" attempted to break into the Republican Guard headquarters in the early hours of Monday and "attacked security forces."
The Muslim Brotherhood's Freedom and Justice Party (FJP), however, issued an official statement saying "peaceful protesters were performing the Fajjr (dawn) prayers" when the army "fired teargas and gunshots at them without any consideration for the sanctity of prayers or life."
"This is also a violation against people's right to peaceful protest," it added.
Large numbers of women and young people sought shelter in a nearby mosque, the Brotherhood statement said, but the security forces "besieged the mosque and arrested anyone who came out of it."
"This has never happened before in the history of the Egyptian army," the FJP statement added.
"Perhaps there are still some wise men in the army who can put a stop to this behavior which is abnormal to the Egyptian army."
The army, however, said it had arrested at least 200 people who had "large quantities of firearms, ammunition and Molotov cocktails."
It also said that it had reopened Salah Salem Road which had been blocked by pro-Morsi protesters.
At a press conference later in the day, military spokesman Ahmed Aly said that pro-Morsi protesters, who have been gathering outside the Republican Guard headquarters for days, used live ammunition and bird shots against security personnel.
He added that at the time of the attack, another group was shooting from atop a building on Al-Tayaran street, where the military facility is located.
"A colleague is in Maadi hospital undergoing a four-hour surgery; he was shot with live ammunition to the head, which caused his skull to fracture," said Aly, who stressed the officer's injury proves that there was firing from building rooftops.
The spokesman also criticised footage circulating on satellite channels of Islamist protesters holding bullet casings and claiming they were fired by the army.
Aly stated that the ammunitions were fake, adding that it isn't possible that the bullets were fired by security forces given that once a bullet is shot, the casing falls next to the shooter.
He also denied pro-Morsi protester's claims that the military killed any children.
"Religious groups spread pictures showing children [killed]...how could children have been involved in that hour of the night," said Aly, who added that the pictures used were of Syrian children taken in March 2011.
President Morsi was deposed by Egypt's Armed Forces on Wednesday following nationwide protests calling for his ouster. Judge Adly Mansour, the head of the High Constitutional Court, was sworn in as the country's interim president on Thursday.
Morsi's removal sparked anger among his supporters, mainly Islamists, spearheaded by the Muslim Brotherhood.
The National Alliance for Supporting Legitimacy, a pro-Morsi group formed to back his right to complete his term of office, continues its sit-in at Rabaa Al-Adawiya Mosque in Cairo’s Nasr City district.
Other pro-Morsi groups have been protesting elsewhere, most notable at Nahdet Misr Square in Giza.
Political reactions and fallout
Shortly after the deadly clashes, Strong Egypt Party leader Abdel-Moneim Abul-Fotouh, a critic of former President Morsi, called on interim president Adly Mansour to step down.
Abul-Fotouh, who resigned from the Muslim Brotherhood shortly after the 2011 uprising, told Al Jazeera that the incident was "a horrible crime against humanity and all Egyptians."
Also on Monday, the Salafist Nour Party, which had initially backed the ouster of President Mohamed Morsi, announced that it "will withdraw from the political process" in response to the incident.
"We wanted to avoid bloodshed, but now blood has been spilled. So now we want to announce that we will end all negotiations with the new authorities," Nour added.
Meanwhile, Constitution Party leader Mohamed ElBaradei has called for an independent investigation into clashes at the Republican Guard headquarters that left at least 42 dead on Monday morning.
"Violence begets violence and should be strongly condemned," ElBaradei said via Twitter. "Independent investigation a must. Peaceful transition is only way."
Egypt's largest opposition coalition, the National Salvation Front (NSF), has expressed its "deep sorrow" over the death of dozens of people outside the Republican Guard barracks.
In a statement it issued on Monday afternoon, the NSF condemned "all acts of violence," including assaults on military barracks and army officers.
Al-Azhar, Egypt's 1000-year-old seat of Islamic learning, has condemned the "painful incident," which it says will portend a dark time of strife.
Egypt's Rebel campaign, the main force behind calls for the 30 June protests culminating in Morsi's ouster last Wednesday, condemned what it perceived as vengeful attempts by political Islamists against the army.
Mohab Doss, a group's spokesman, claimed the incident was a "reaction" by the army to "intimidation" by Islamist groups.
However, Doss added "the whole truth of what really happened should be uncovered through an independent investigation."