Egyptian officials say fighting between police and Islamic supporters of ousted president Mohamed Morsi has killed at least 50 people and injured more than 200.
Most of the violence took place in Cairo. Street battles erupted between the Islamists and pro-military marchers celebrating a national holiday for the 40th anniversary of the Arab-Israeli war.
Both sides exchanged rocks, gasoline bombs, and light gunfire. Police used tear gas to drive away the Morsi supporters.
Sunday's violence was some of the worst since the August crackdown on Morsi supporters that killed hundreds.
Egypt's military-backed interim government hoped to use Sunday's holiday to highlight popular support for military leader General Abdel Fatah el-Sissi. But the pro-Morsi Muslim Brotherhood organized its own marches under the banner "Reject the Coup."
The military overthrew President Morsi in July and installed an interim government with the promise of rewriting the constitution and holding new elections.