Opposition protesters clashed with Islamists near Muslim Brotherhood headquarters in Cairo on Friday after activists marched to the building guarded by police and members of Egypt's ruling movement.
Gunshots were heard as hundreds of opposition activists and the Islamists battled in the streets of the Mokattam neighbourhood where the headquarters are situated.
Police had fired tear gas at the protesters outside the headquarters before the clashes moved elsewhere in the neighbourhood.
Protesters captured and beat three Brotherhood members. They also smashed up an ambulance evacuating a wounded Brotherhood supporter and detained him, an AFP correspondent said. Dozens were wounded by stones.
In Manial, a middle-class island on the Nile, men ransacked an office belonging to the Islamists and assaulted women holding an event marking Mother's Day, Brotherhood spokesman Ahmed Aref told AFP.
"They trapped the women in the toilets and then destroyed the office's contents and threw them out onto the streets," Aref said.
As the clashes rumbled on, live television showed hundreds of protesters carrying anti-Brotherhood banners and making their way up to the hilly Mokattam neighbourhood.
Opposition activists had called for the protest a week after they battled with the Islamists near the Brotherhood headquarters. The movement vowed on Thursday it would protect its headquarters and bused in hundreds of supporters.
Primarily, "the protection of private and public property is the responsibility of the police," the group's secretary general Mahmud Hussein told a news conference.
"But the owner of every house has the right to defend it using all means. If the police don't carry out their responsibility, we will protect our property with all we posses," he added.
The Brotherhood has seen about 30 of its offices across the country attacked in widespread protests against President Mohamed Morsi, the Islamists' successful candidate in last June's election.
The Brotherhood, well-organised despite decades of persecution under former strongman Hosni Mubarak and his predecessors, was the main winner of parliamentary and senate elections last year.
But its critics accuse it and Morsi of mirroring the tactics used by Mubarak against the opposition.
The Islamists clashed before with opposition activists, most notoriously in December when at least 11 people were killed in clashes outside the presidential palace after Morsi adopted extensive powers, since repealed.