Thirty eight people have been killed in clashes between security forces and supporters of the ousted Islamist president, Egypt’s health ministry said.
Street battles raged for hours in Cairo, as demonstrators fired birdshot and threw firebombs at police who responded with gunshots and tear gas.
In some cases, pro-military crowds set upon supporters of the former president, Mohammed Morsi, with the two sides pelting each other with rocks.
By late evening, several parts of the city resembled combat zones, with fires burning, black smoke rising and the crack of gunfire piercing the air, thick with tear gas. Streets were strewn with debris. Authorities said 32 died in the capital.
An Associated Press photographer saw nine bodies lying on the floor in the Cairo district of Dokki, scene of some of the heaviest clashes. He said most bodies had gunshot wounds to the head or chest.
The clashes took place on the 40th anniversary of the start of the 1973 Mideast war, a holiday the military-backed government had wanted to use to pay tribute to the armed forces, whose chief ousted Mr Morsi in a popularly supported coup on July 3.
Earlier in the day, soldiers had barricaded entrances to central Tahrir Square with barbed wire and armoured personnel vehicles. Metal detectors were installed at the entrances and demonstrators pouring into the square were searched by troops.