At least 18 people, including three policemen, have died at protests around the country on the fourth anniversary of the 2011 revolution, the health ministry announced Sunday.
Ten people, including a police conscript, were killed in Cairo's Matariya district in the north of the capital, where the day's most intense and sustained clashes took place.
Matariya is a hotbed for clashes between pro-Mohamed Morsi protesters and police, with weekly confrontations typical and deaths regularly reported.
By early evening, clashes in Cairo had subsided, with the exception of Matariya.
Another person was killed elsewhere in Cairo and two more in Giza, where the municipality headquarters of the Haram district were torched. Another two police conscripts were killed by unknown assailants in Giza who fled in a car on the ring road through the Moneib district, Egypt's state news agency MENA reported.
One person was also killed in the coastal city of Alexandria, health ministry officials said.
A further two people died when a bomb they were planting detonated in the Nile Delta's Beheira governorate, health ministry official Khaled El-Khateeb told Reuters' Aswat Masriya.
The ministry also said that at least 38 people were injured in clashes in Cairo, Giza, the Nile Delta's Kafr El-Sheikh and Upper Egypt's Minya governorate; the interior ministry said 11 policemen were injured.
The interior ministry said in a statement that close to 150 "rioters" were apprehended on Sunday across the country.
Clashes also erupted on Sunday in downtown Cairo between protesters and a number of supporters of President Abdel-Fattah El-Sisi during a protest at the Journalists Syndicate.
The protest was organised to demand retribution for those injured in the 2011 revolution. Demonstrators had chanted for retribution, as well as chanting against military rule and against El-Sisi.
Clashes started when a group of El-Sisi supporters began to hurl rocks at the protesters. Security forces dispersed the clashes, firing teargas. No deaths were reported.
Security forces also dispersed a protest of about 100 supporters of El-Sisi in downtown Cairo's Abdel-Moneim Riyad Square, Aswat Masriya reported. No one was arrested at the protest.
Earlier in the day, 15 people Morsi supporters were arrested in the same square.
A number of youth groups affiliated with the pro-Mohamed Morsi National Alliance to Support Legitimacy had earlier called for protests in downtown Cairo.
The secular group the April 6 Youth Movement, which was outlawed last April, had also called for protests in a number of downtown squares, including Abdel-Moneim Riyad, Abdeen, Opera, Bab Al-Louk and Talaat Harb, after the killing of socialist activist Shaimaa El-Sabagh at a march on Saturday.
El-Sabagh, 33, was marching with a dozen Socialist Popular Alliance Party members to lay flowers in Tahrir Square in memory of protesters who died in the January 2011 uprising when she was shot. The party said her death was “premeditated murder.”
Security forces have dispersed other small protests nationwide.
More than 60 people were killed in last year's revolution anniversary, around six months after the ouster of Islamist President Mohamed Morsi following mass protests against his rule.