The unrest in Egypt has raised international concerns over the country's stability and prompted a statement from UN Secretary General Ban Ki-Moon.
He condemned both "violent protests" - the Muslim Brotherhood's rallies and the authorities' "excessive use of force".
Mr Ban said, in an apparent rebuff of Brotherhood demands to reinstate deposed president Mohammed Morsi, that the "political clocks move only forward, not backward" and urged "maximum restraint and shift immediately to de-escalation".
On Saturday, Egyptian security forces stormed a Cairo mosque after a heavy exchange of gunfire with armed men shooting down from a minaret. They rounded up hundreds of supporters of the country's ousted president who had sought refuge there overnight after violent clashes killed 173 people.
The raid on the al-Fath mosque on Ramses Square was prompted by fears that Mr Morsi's group again planned to set up a sit-in, security officials said, similar to those that were broken up on Wednesday in assaults that killed hundreds of people.
The brother of al-Qaida chief Ayman al-Zawahri was arrested in connection to the raid on the mosque. Officials said that he planned to bring in armed groups to provide support to those holed up inside the mosque.
Mohammed al-Zawahri, a Morsi ally, is the leader of the ultraconservative Jihadi Salafi group which espouses al-Qaida's hardline ideology. He was detained at a checkpoint in Giza, the city across the Nile from Cairo, the official said.
The Egyptian government meanwhile announced it had begun deliberations on whether to ban the Muslim Brotherhood, a long-outlawed organisation that swept to power in the country's first democratic elections a year ago. Such a ban - which authorities say is rooted in the group's use of violence - would be a repeat of the decades-long power struggle between the state and the Brotherhood.
For more than a month, since the July 3 military overthrow of Mr Morsi, Brotherhood members and supporters have attacked and torched scores of police stations and churches, in retaliation. Shops and houses of Christians have also been targeted.
Such attacks spurred widespread public anger against the Brotherhood, giving the military-backed government popular backing to step up its campaign against the Islamist group. It reminded people of a decade-long Islamist insurgency against Mubarak's rule in the 1990s which only strengthened security agencies and ended up with thousands of Islamic fundamentalists in prisons.