Egypt's interim administration has expressed "deep regret" after gunmen opened fire on supporters of deposed Islamist President Muhammad Morsi, killing more than 50 people.
State television reports that interim leader Adli Mansour has formed an investigative commission to look into the incident, which took place during a sit-in early on July 8 outside the Republican Guard facility where it is believed Morsi is being held.
Emergency services said that more than 430 people were wounded, while the army said that two police and one army officer were killed in the clashes.
Pro-Morsi demonstrators blame the military for the attack.
"I was outside the [military] barracks, near the entrance, and I saw people coming at me, so I looked over my shoulder so that I could run. But when I turned back to the front, a tear-gas canister hit me in the face," Muhammad Ali, who was among the wounded protesters, told Reuters.
"Blood was coming out of my face, so I lay down on my back. Then a soldier attacked me and hit me on the leg with the butt of his rifle and said they had to clean the square of all of us that day."
The military, however, says it was "armed terrorists" who fired on the crowd. News agency dpa reports the army has arrested 200 people for attempting to storm the facility, reportedly armed with guns, Molotov cocktails, and other weapons.
The continued chaos has thrown the fate of the Arab world's largest state in doubt.
Following the reports of the violence on July 8, the European Union called for a return to the democratic process as soon as possible. Michael Mann, the spokesman for EU foreign-policy chief Catherine Ashton, said the EU was "talking to everyone on the ground to make sure everyone understands the need for peace to be maintained."
Germany's Foreign Ministry called for an independent investigation into the killings.
Qatar condemned acts "that take away innocent lives." Iran has called the Egyptian Army's interference in politics "unacceptable" and blamed Israel and the United States for the problems that started in Egypt last week.
Chaos, Fighting In The Streets
The attack comes five days after the military overthrew Morsi following mass nationwide demonstrations calling for his resignation.
Morsi's opponents blamed him and his Muslim Brotherhood movement for economic stagnation and said it was trying establish authoritarian rule.
The Muslim Brotherhood denounced Morsi's removal as a coup and has called for an "uprising."
The July 8 casualties come after at least 35 people were killed across Egypt on July 5 and 6 as clashes raged between pro- and anti-Morsi demonstrators.
In an attempt to impose calm, military vehicles in the capital, Cairo, have sealed off traffic in a wide area surrounding the Rabaa Adawia Mosque, where Morsi supporters have been gathering since his ouster.
The army has also used armored vehicles to close off two of the main bridges spanning the Nile River.
The continued violence comes as attempts at forming a new government have foundered.
The hard-line Salafist Nour party, which backed Morsi's ouster, has pulled out of negotiations in protest over what it called the "massacre" on July 8.
The participation of Nour, Egypt's second-biggest Islamist party, is considered essential to the legitimacy of any new government.
Nour had already refused to back the candidacy of liberal politician Muhammad ElBaradei for prime minister.
Officials had hoped to instead appoint a social-democratic lawyer, Ziad Bahaa el-Din, as interim prime minister.
ElBaradei on July 8 condemned the latest violence, writing on Twitter that "Egypt is in dire need of reconciliation."