The bloodshed came as many Egyptians were celebrating the 40th anniversary of the 1973 war with Israel. The New York Timesreports:
"As the military's supporters celebrated the anniversary in Tahrir Square in Cairo with music and fireworks, officers and armed civilian loyalists set upon Islamist protesters who were also trying to reach the square, driving back their marches with tear gas and gunfire."
NPR's Fadel reports that as gunfire rang out, it was often unclear who was shooting. In addition to the deaths, she says hundreds supporters of ousted President Mohammed Morsi were arrested, accused of instigating riots.
The fighting is the latest in a series of clashes between security forces and the Islamist group that put Morsi in power. Since July, hundreds of Brotherhood members have been killed and most of the movement's leaders have been sent to jail or fled the country.