Leading Muslim Brotherhood member Abdel-Rahman El-Bar addressed tens of thousands of President Mohamed Morsi's supporters outside Cairo's Rabaa Al-Adawia Mosque on Friday calling for peaceful protests after at least four Islamist demonstrators were killed in clashes across Egypt.

"We know that the voice of peace is louder than that of the gun," he said. "We are one nation...we are all Egyptians and no one can exclude the other."

El-Bar condemned the recent killing of Muslim Brotherhood members during recent clashes in different Egyptian governorates.

He said: "We are concerned about this nation...we will not shed blood and we will continue to raise the banner of peace... Building a nation can only be accomplished by a free people, not thugs."

The prominent cleric also warned of attempts to "overturn democracy," assuring the crowds that Egypt's state institutions were continuing to work "to protect democratic legitimacy." He dismissed claims that Egypt's security forces were backing the opposition.

El-Bar went on to slam Egypt's opposition for rejecting invitations to dialogue issued by the presidency.

"Your incitement of violence will always haunt you," he said of leaders of the opposition. "The people will not forget those who incited against Islam and incited violence."

Last Friday saw massive pro-Morsi demonstrations in the same location in response to opposition calls for snap presidential elections.

Meanwhile, tens of thousands demonstrated in Tahrir Square against the president, while thousands more marched across Cairo. Alexandria, Daqahliyah, Gharbiya and Aswan also witnessed opposition protests on Friday.

Several Muslim Brotherhood offices and pro-Morsi demonstrations throughout Egypt have been attacked within the past week amid calls for Sunday's anti-Morsi protests.

On Friday, anti-Morsi protesters attacked Brotherhood offices in Alexandria, Daqahliya, Gharbiya, Kafr Al-Sheikh and Beheira.