Tens of thousands of supporters of president Mursi have been converging in Rab'a al-Adawiay square.
Today's demonstration is aimed at pre-empting mass protests planned by the opposition on Sunday, the anniversary of Mursi's inauguration.
On the other hand protesters took to the streets in several cities in Egypt to object to the Muslim Brotherhood and Mursi.
Clashes erupted in the coastal city of Alexandria where rubber pellets and stoned were used to disperse protesters. As a result more than 200 were injured.
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The ministry of interior has kept its promise of keeping a distance from both sides but protesters reported several officers were giving them a thumbs-up as they passed them.
The authorities are reported to have called in riot police and army helicopters to try to quell the violence.
The preacher delivering the sermon at the Friday prayers in Rab'a square accused the opposition of being against religion in addition to being against the president.
Military tanks were deployed in the streets of Cairo a few days ago around the main establishments including the central bank and the presidential palace.
Rebellion campaign, which started three months ago collecting signatures by Egyptians to withdraw support from President Mursi, claims it has so far gathered more than 15 million signatures and therefore can strip him of his legitimacy.
Their plan was to take to the street on June 30, the day Mursi would complete a year in power.
But Mursi supporters said they would fill the squares as of June 28 to abort the planned protests by opposition.