Egyptian security forces have entered a mosque in the capital, Cairo, to try to persuade Muslim Brotherhood supporters barricaded inside to leave.
Dozens remain, refusing to believe the authorities’ pledge of a safe exit.
The tense stand-off follows a day of bloody clashes on Friday in which more than 80 people died and 1,000 Brotherhood supporters were arrested.
The group has called for daily protests after a crackdown on their camps in Cairo on Wednesday left hundreds dead.
The Brotherhood is demanding the reinstatement of Mohammed Morsi – Egypt’s first democratically elected president – who was removed by the army last month and replaced with an interim government.
Fear for lives
On Saturday, police surrounded the al-Fath mosque in Cairo’s Ramses Square, where Morsi supporters were holed up.
Security forces then entered the building to try to persuade them to leave.
Live television pictures showed security forces in riot gear on the steps outside, but with no sign of violence.
The security forces did fire into the air to keep protesters away as a small group of women was escorted from the mosque.
Many Morsi supporters have left, but correspondents say dozens remain in the main hall, refusing to go.
BBC Arabic spoke to two of the protesters inside who said that they feared for their lives.
They told the BBC that they did not trust the authorities’ promises of a safe exit.
They said there were two bodies inside – one of them of a woman who died after tear gas was fired by police into the mosque overnight and another of a man taken into the building after sustaining bullet wounds.
They said the protesters had drinking water but there was only one toilet.
Some 1,000 people were trapped in the mosque after violence in Ramses Square on Friday.
Security officials quoted by the official Mena news agency said “armed elements” had opened fire from inside the mosque.
The building quickly filled with dead and injured – as well as those fleeing the violence.
Egypt’s interior ministry said in a statement on Saturday that 1,004 “Muslim Brotherhood elements” had been arrested on Friday, 558 of them in Cairo.
‘Day of anger’
The Muslim Brotherhood has been on the streets since the army deposed Mr Morsi on 3 July.
On Wednesday at least 638 people died when the Brotherhood’s two protest camps in Cairo were cleared, a move that sparked international condemnation.
Friday’s protests – dubbed a “day of anger” – were called in response to Wednesday’s bloodshed. Most of the latest deaths were in Cairo but about 40 elsewhere.
Egypt’s interim leaders have imposed a state of emergency, with dusk-to-dawn curfews in the capital and other areas. The interior ministry says police have been authorised to use live ammunition “within a legal framework”.
Correspondents say the atmosphere in Cairo is tense, with many armoured personnel carriers deployed on the streets.
The army has blocked off all entrances to Tahrir Square – the focus of demonstrations that led to the toppling of President Hosni Mubarak in 2011.
Meanwhile, groups that support the army-backed interim government – the National Salvation Front and Tamarod – are calling for counter-demonstrations in response to the Muslim Brotherhood protests.
Friday’s violence erupted shortly after midday prayers when thousands of Morsi supporters answered the Brotherhood’s call for rallies across Egypt.
Witnesses said armed civilians were among those who clashed with protesters, while vigilantes set up roadblocks in some areas to stop Brotherhood supporters getting through.
Elsewhere in Egypt, at least 21 people were killed in the second city of Alexandria, six in Suez, eight in Damietta and five in Fayoum, according to medical sources.
Mr Morsi is now in custody, accused of murder over a 2011 jailbreak. His period of detention was extended by 30 days on Thursday, state media said.