Angry supporters of ousted Islamist President Mohammed Morsi clashed Friday with Egyptian police, who have orders to use live ammunition against the protesters.
At least 17 people have died in the fresh round of violence. Most of the deaths have occurred in Cairo, Egypt's capital.
Thousands of Morsi supporters gathered in Ramses Square in central Cairo after Friday prayers to protest his ouster — a rally called for by the Muslim Brotherhood, the Islamist group from which Mr. Morsi hails. They also are protesting a crackdown Wednesday by security forces on two pro-Morsi sit-ins in Cairo that claimed the lives of more than 600 people.
The crackdown unleashed violence across Egypt that has included attacks on government buildings and churches.
Egyptian security forces deployed near government buildings in Cairo and Giza on Friday, as Morsi supporters issued a call for "Friday of Rage" protests.
There were conflicting reports on the death toll from Wednesday's crackdown.
Egypt's Health Ministry said Thursday that 638 people had died, but Muslim Brotherhood spokesman Gehad El-Haddad put the death toll at more than 4,000.
The Interior Ministry said 43 policemen had been killed Wednesday in clashes.
Mr. El-Haddad said that at least five Brotherhood officials had been injured Wednesday, but he declined to disclose their identities. No Brotherhood leaders were killed.
U.N. High Commissioner for Human Rights, Navi Pillay, said the death toll, "even according to the government's figures, point to an excessive, even extreme, use of force against demonstrators."
She called for an impartial and credible investigation into the conduct of security forces.
Mr. Morsi has been detained at an undisclosed location since the military toppled his government on July 3 following four days of anti-government protests that brought millions of Egyptians onto the streets of Cairo.
Army Chief Gen. Abdel Fattah el-Sisi replaced Mr. Morsi with an interim government and appointed Adly Mansour, chief justice of the constitutional court, as interim president.
The Brotherhood's political wing, the Freedom and Justice Party, said on Friday that it was an "obligation" to topple the "illegitimate regime." It said it would not back down from protests, but that these would be peaceful.
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