At least six people were killed in clashes between pro-Islamist protesters and Egyptian police in Cairo on Friday, the health ministry said.
Supporters of ousted Islamist president Mohamed Morsi had held small marches after the morning prayers for Eid al-Fitr, which marks the end of the holy Muslim fasting month of Ramadan.
Police officials said the protesters attacked security forces stationed in Cairo's Talbiya district near the Giza pyramids. The health ministry did not give a breakdown of those killed. Protest clashes were also reported in the village of Nahya near Cairo.
In the Mediterranean city of Alexandria, police arrested 20 Islamist protesters after they directed fireworks at policemen, the official MENA news agency reported.
Pro-Morsi protests have dwindled since his ouster by the military in 2013, which led to a massive crackdown on Islamists that killed at least 1,400 people in street violence. Hardcore supporters continue to hold small protests that are often confined to one or two Cairo neighbourhoods. Demonstrations have largely given way to militant attacks, often small bombings and attacks on infrastructure such as electricity towers.
In the Sinai Peninsula, jihadists affiliated to the Islamic State group have killed hundreds of policemen and soldiers in an insurgency since Morsi's overthrow. Morsi's Muslim Brotherhood has been blacklisted and thousands of its sympathisers have been jailed.
Hundreds, including Morsi, have been sentenced to death. Most have appealed the verdicts and won retrials. Protesters risk jail even for non-violent demonstrations under a law that requires obtaining a police permit to demonstrate.
The crackdown has gutted the Muslim Brotherhood, once Egypt's largest political movement. The Islamists had been banned for decades until a popular 2011 uprising ousted veteran strongman Hosni Mubarak. They went on to dominate parliament and then win the 2012 presidential election with their candidate Morsi, who lasted only a year in office.
The Islamist proved to be a divisive leader, prompting millions to demonstrate against him demanding his resignation. The crackdown on the Brotherhood has shown no signs of letting up, with weekly arrests of the group's remaining organisers in Egypt.
Many of the group's leaders had fled the country and operate out of Turkey and the United Kingdom. Earlier this month, police killed nine mid-level and senior members of the Brotherhood in a raid on an apartment in Cairo as they were holding a meeting. Police say they came under fire when they tried to arrest the men.