At least seven people have died in overnight clashes between supporters of ousted Egyptian president Mohamed Morsi, opponents and security forces, officials said.
Mohamed Sultan, the head of Egypt's emergency services, said more than 260 people were injured in the latest eruption of violence since the military unseated Mr Morsi, just a year after he was elected.
More than 400 people were arrested, according to the state news agency.
Two people were killed at a bridge in in the Ramses area near Tahrir Square in Cairo, where security forces reportedly fired tear gas to drive the protesters back.
The protesters responded by hurling rocks at the security forces, triggering fresh volleys of tear gas, with clashes continuing in adjacent Ramses Square and elsewhere late into the night.
Five more people died in the capital's Giza district, Mr Sultan said.
Security officials said four of the deaths came as Morsi supporters staging a sit-in near the main Cairo university campus clashed with residents of the area.
Thousands of supporters of the former president were calling for him to be reinstated.
Mr Morsi's Muslim Brotherhood said the police used birdshot and live ammunition against the protesters.
Many protesters were treatment at a makeshift ward set up to deal with casualties.
The deputy president of the Muslim Brothehood's political party, Essam el Erian, had stressed the protests and sit-ins must remain peaceful.
"The fact that our protests are peaceful is what makes them powerful," he said.
"We will remain peaceful in our path to continue the January 25 revolution and we will not use violence to respond to the violence that targets us."
Meanwhile, a spokesman for Egypt's interim president said the authorities expect Islamist movements, including the Muslim Brotherhood, to join in plans for a national reconciliation government.
A senior official in the movement said they had not been offered any posts in the transitional government by interim Prime Minister Hazem el Beblawi and would not accept if he did.