Egypt's ruling Muslim Brotherhood deputy leader on Saturday said opponents have taken to violence after proving incapable at politics, a day after vicious clashes outside the Islamists' headquarters.
Rashad al-Bayoumi, the Brotherhood's deputy Supreme Guide, said Friday's violence that wounded more than 160 people was "a tragedy."
"If it proves anything, it points to a type of vile character. I hold those who called for such protests politically and legally accountable," he told AFP.
"This announces the failure of those people to conduct a clean political confrontation, so they had resorted to these despicable means," he said.
The Brotherhood on Saturday circulated footage of its members being beaten, burned with petrol bombs and stabbed during Friday's clashes, which began after hundreds of opponents marched on the Islamists' Cairo headquarters.
The group called on security forces to crackdown on those responsible for the violence.
"Only God knows the extent of anger and frustration in the Brotherhoods' heart," it said in a statement. "It is time for security forces to forcefully strike the perpetrators."
Police used tear gas against the protesters before the clashes spilled over elsewhere in the normally calm Cairo neighbourhood of Mokattam.
Riot police trucks lined the street outside the headquarters on Friday.
Mohamed ElBaradei, an opposition leader who formerly headed the UN's nuclear watchdog, blamed the government and police.
"Violence begets violence, and the tragedy of the nation won't be solved through violence. The regime is responsible for protecting citizens and treating the reasons for violence," he wrote on Twitter.
Another opposition leader, former Arab League chief Amr Mussa, denounced the clashes.
"We all reject violence, and we cannot accept counterviolence," he wrote on Twitter.
The Brotherhood has seen about 30 of its offices across the country attacked in widespread protests against Islamist President Mohamed Morsi.
Well-organised despite decades of persecution under former strongman Hosni Mubarak and his predecessors, the Brotherhood was the main winner of parliamentary and senate elections last year.
However, its critics accuse both it and Morsi of mirroring tactics used by Mubarak against the opposition.
In the bloodiest violence between Morsi's supporters and his opponents, at least 11 people were killed in clashes outside the presidential palace in December after Morsi adopted extensive powers.
He later rescinded his sweeping prerogatives, after rushing through a Islamist drafted constitution in a referendum.