Egyptian authorities rounded up more than 1,000 Islamists as the Muslim Brotherhood leadership defiantly called a week of nationwide protests starting on Saturday after a day of carnage.
After Friday's bloodshed in which more than 100 people died in clashes that pushed Egypt ever closer to anarchy, tensions were high with supporters of ousted Islamist President Mohamed Mursi in a Cairo mosque where bodies had been taken during the violence, while security forces were stationed outside.
The interior ministry said that 1,004 Muslim Brotherhood "elements" had been arrested, accusing members of Mursi's movement of committing acts of terrorism during the clashes, which took the deathtoll to 700 since Wednesday.
The Brotherhood, which ruled Egypt for a year until the army removed Mursi on July 3, urged its supporters back onto the streets to denounce the military takeover and the subsequent crackdown on followers of the nation's first freely-elected president.
"Our rejection of the coup regime has become an Islamic, national and ethical obligation that we can never abandon," said the Brotherhood, which hasaccused the military of plotting the downfall of Mursi last month to regain the levers of power.
Many Western allies have denounced the killings, including the United States, but Saudi Arabia threw its weight behind the army-backed government on Friday, accusing its old foe the Muslim Brotherhood of trying to destabilise Egypt.
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Violence erupted across Egypt after the Brotherhood, which has deep roots in the provinces, called for a "Day of Rage". Roughly 50 people died in Cairo and more that 20 in the country's second city, Alexandria, security sources said.
Automatic gunfire echoed around the capital throughout Friday afternoon, army helicopters swooped over the roof tops and at least one office block was set ablaze, lighting up the night sky long after the violence had subsided.
The Brotherhood announced a series of daily rallies over the next six days, starting on Saturday.
"We will not leave the squares. And we will not be silent over our rights, ever," said Cairo resident Abdullah Abdul Fattah, adding that he was not a Brotherhood voter.
"We are here because of our brothers who died," he said. An interim cabinet, installed by the army after it removed Mursi during rallies against his often chaotic rule, has refused to back down. It has authorized police to use live ammunition to defend themselves and state installations.
After weeks of futile, political mediation, police moved on Wednesday to clear two Brotherhood protest sit-ins in Cairo. Almost 600 people, most of them Islamists, were killed in the mayhem. With no compromise in sight, the most populous Arab nation - which is often seen as leading events in the entire region - looks increasingly polarised and angry.