Group has called on pro-Morsi supporters to stage "anti-coup rallies" after Friday prayers to protest deadly crackdown.
The announcement comes a day after hundreds of people were killed when security forces cleared two pro-Morsi protest camps, ending sit-ins that began after the army toppled Morsi on July 3.
"Anti-coup rallies tomorrow will depart from all mosques of Cairo and head towards Ramsis square after Jumaa prayer in 'Friday of Anger'," Muslim Brotherhood spokesman Gehad el-Haddad wrote on his Twitter account.
The health ministry spokesman yesterday said death toll from nationwide violence in Egypt has climbed to 638, making it the bloodiest day since the Arab Spring in 2011 toppled longtime President Hosni Mubarak in a popular uprising.
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Officials from the Muslim Brotherhood have said the death toll was eight or nine times higher than the government figures.
Muslim Brotherhood said it suffered a strong blow from the state security crackdown and the bloodshed means anger is now "beyond control".
But, defiant Morsi supporters attacked the local government offices in Giza and set them ablaze. Television footage showed the headquarters in flames as men tried to douse the fire with hoses. Assailants used Molotov bombs to burn down the building.