Gunfire has erupted around a Cairo mosque where hundreds of supporters of ousted President Mohamed Morsi have barricaded themselves inside.
Video from the scene showed security forces shooting toward Al-Fatah Mosque near Ramses Square, and chaos inside the building as people took cover.
Reporters at the scene said security forces exchanged fire with someone firing at them from above, inside the mosque's minaret, but it it is unclear who fired first.
A standoff between security forces outside and protesters inside the mosque had been in effect for hours before the gunfire began at midday. The protesters are supporters of Morsi's Muslim Brotherhood movement.
Crowds of civilians milled about outside the mosque. Reporters there said many are opponents of the Brotherhood, whose activists they denounced as "terrorists."
Interim Prime Minister Hazem el-Beblawi said the government aims to achieve "harmony and reconciliation." But he added, that would not include those whose "hands are stained with blood."
Egypt's latest crisis began Friday, when thousands of Muslim Brotherhood supporters took to the streets for "Day of Rage" protests, and clashes broke out between demonstrators and security forces - in Cairo and in other cities around the country.
An Egyptian government spokesman said Saturday that the previous day's carnage left 173 people dead and more than 1,000 injured. Speaking to reporters in a session broadcast nationally, the spokesman said 57 security force officers were among the dead, and that Cairo had the greatest number of deaths - 95.
The spokesman accused the Muslim Brotherhood of magnifying the number of victims, and said Brotherhood supporters had assaulted police stations, prisons and churches.
The government official, Shereef Shawki, said are considering legally disbanding the Brotherhood.
More than 700 people have been killed since government forces began a crackdown Wednesday on two pro-Morsi encampments operating in Cairo for weeks. The Muslim Brotherhood contens the actual death toll was in the thousands. The Muslim Brotherhood has insisted it would hold more protests.