Around 500 people gathered near the Muslim Brotherhood's headquarters in Cairo's Moqattam district, hurling Molotov cocktails and stones at the building, state news agency MENA reported Sunday evening, quoting eyewitness as saying they had heard shots during the melee.
Television channels aired images of parts of the building exterior in flames.
A senior official of the Brotherhood's Freedom and Justice Party (FJP), Gehad El-Haddad, lamented the attack on Twitter.
"No police on scene yet in Moqattam. Security is dealing w/ attacking thugs. They were joined by others wearing Black Bloc uniform w/ firearms," he asserted.
A number of offices belonging to the Brotherhood and the FJP, the group's political arm, have been attacked in recent days.
