The Cairo headquarters of Egypt's ruling Muslim Brotherhood was overrun by youths who ransacked the building after those inside had been evacuated on Monday following a night of violence.
Security sources said five people were killed in hours of fighting around the besieged building.
Medical sources said over 100 were wounded.
Reuters journalists saw youths hurl petrol bombs and rocks at the offices. Guards inside opened fire.
By Monday morning, people inside were still firing on youths outside. Reuters journalists saw two men hit.
A Brotherhood spokesman later said that the movement had evacuated staff from inside.
Live television pictures showed men inside, throwing equipment out of scorched windows. One flew an Egyptian flag from a balcony.