Many casualties are reported after Egyptian security forces moved in with armored vehicles, bulldozers, tear gas and snipers to clear two protest camps in Cairo set up by supporters of ousted President Mohamed Morsi.
Widely divergent estimates of the death toll have emerged amid the confusion. The French News Agency reported 124 people died the crackdown. The Muslim Brotherhood called the operation a "massacre" and said the death toll is in "the hundreds." State television said six members of Egypt's security forces were killed and 66 wounded.
Witnesses and foreign journalists reported live fire from security forces' shotguns and automatic rifles, while the army released photos of pro-Morsi supporters using weapons against security forces. Scores of people were arrested, including Brotherhood leaders.
Unrest quickly spread beyond the capital to the cities of Minya and Assiut and Alexandria. Five people were killed in Suez.
In a televised statement, a government spokesman blamed the violence in Cairo on the Muslim Brotherhood and hailed police for their "professionalism."
"The government demands the political leadership of the Brotherhood stop incitements to violence and holds these leaders fully responsible for any blood that is shed. The government also salutes the efforts of the security services for...using the utmost self-restraint and highest degree of professionalism in the operation to clear the sit-in."
A number of countries, including Britain, Turkey and Qatar quickly condemned the use of force by Egyptian authorities and called for restraint from the security forces.
Hours after the operation began, authorities said they had cleared one of the encampments at Nahda Square near Cairo University.
But protesters at the larger camp around the Rabaa al-Adawiya mosque in the eastern suburb of Nasr City remained under siege. Television footage showed smoke rising over the protest site and military helicopters circling in the sky.
Egypt's railway authority said train service in and out of Cairo has been suspended to keep activists from regrouping elsewhere.