Egypt's Health Ministry said that six people were killed and at least 36 injured in various incidents across Egypt on Friday. Reports later in the day suggested as many as 190 had been injured.
Tens of thousands of demonstrators and pro-Morsi supporters took to the streets on Friday in smaller, more scattered protests than those seen in recent weeks.
Muslim Brotherhood leaders have been urging supporters to protest the police crackdown that killed hundreds of people earlier this month.
In the city of Port Said, one protester was killed and 21 were injured in clashes, according to a ministry official in the city.
It was not immediately clear where or how the other casualties took place.
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In Cairo, protesters gathered into smaller groups and avoided the larger public squares where police and tanks have been deployed.
According to the Associated Press, Muslim Brotherhood supporters joined with protesters seeking justice for relatives killed by security forces this month.
The Aug. 14 crackdown is said to have killed at least 600 people.
As they marched, protesters chanted slogans against Egyptian army chief Gen. Abdel-Fatah el-Sisi, who led the July 3 coup that ousted President Mohamed Morsi, a longtime leader of the Muslim Brotherhood.
"The people want the death of the assassin!" the demonstrators yelled, according to the AP.
"When it started, it was only about the return of Morsi to power," one protester, Ahmed Osama, said. "Now it has gone past that. Blood has been shed."
Reuters reported that marches were also held in several cities in the Nile Delta, including Tanta and Fayoum; in the three Suez Canal cities of Suez, Ismailia and Port Said; and in the southern city of Assiut.
More than 10,000 protesters took part in several separate demonstrations in Egypt's second largest city, Alexandria.