Updated at 10:28 a.m. ET
CAIRO Witnesses say that Egyptian security forces have stormed a Cairo mosque after firing tear gas at hundreds of Islamist supporters of the country's ousted president barricaded inside.
Local journalist Shaimaa Awad told The Associated Press on Saturday that security forces rounded up protesters inside al-Fatah mosque, located in Cairo's central Ramses Square.
The sound of gunfire could be heard in the background.
Abigail Hauslohner, Cairo bureau chief for The Washington Post, told Al Jazeera English that it was uncertain how the fight at the mosque broke out.
"I have no idea the extent to which people in the mosque are firing back or whether this is mostly an onslaught from security forces," said Hauslohner. "It's difficult to tell. Obviously the security forces are very, very well-armed."
Egypt's official news agency MENA reported that gunmen opened fire on security forces from the mosque's minaret. Local television stations broadcast live footage of soldiers firing assault rifles at the minaret.
CBS News correspondent Charlie D'Agata reported from Cairo on "CBS This Morning: Saturday" that security forces had begun to allow people to leave that mosque where they had been trapped overnight; however, many of the roughly 1,000 supporters of Islamist President Mohammed Morsi's Muslim Brotherhood continued to remain inside the mosque.
They sought shelter at the mosque fromand found themselves there after a state-imposed curfew, D'Agata reports.
The mosque served as a field hospital and morgue following clashes Friday in the area. The protesters barricaded themselves inside overnight out of fears of being beaten by vigilante mobs or being arrested by authorities.
D'Agata reports that the Brotherhood called out for supporters to converge on the mosque and help "free their brothers."
Earlier, protesters vowed to defy a state of emergency with new protests on Saturday. Friday's marches in Cairo.
An Egyptian government spokesman said Saturday that 173 people were killed Friday in what the Muslim Brotherhood called a "Day of Rage" ignited by anger at security forces for.
Across the city Friday, police and armed vigilantes at neighborhood checkpoints battled Muslim Brotherhood-led protesters, with the sight of residents firing at one another marking a dark turn in the conflict.
Military helicopters hovered over downtown as residents furious with the Brotherhood protests pelted marchers with rocks and glass bottles. The two sides also fired on one another, sparking running street battles throughout the capital's residential neighborhoods.
The violence capped off a week that saw more than 700 people killed across the country. That toll surpasses the combined death toll from two and a half years of violent protests since the ouster of longtime leader Hosni Mubarak to, who hails from the Brotherhood.
Unlike in past clashes between protesters and police, Friday's violence introduced a combustible new mix, with residents and police in civilian clothing battling the marchers.
Few police in uniform were seen as neighborhood watch groups and pro-Morsi protesters fired at one another for hours on a bridge that crosses over Cairo's Zamalek district, an upscale island neighborhood where many foreigners and diplomats live.
Friday's violence erupted shortly after midday prayers when tens of thousands of Brotherhood supporters answered.
Armed civilians manned impromptu checkpoints throughout the capital, banning Brotherhood marches from approaching and frisking anyone wanting to pass through. At one, residents barred ambulances and cars carrying wounded from Ramses Square from reaching a hospital.
Several of the protesters said they were ready to die, writing their names and relatives' phone numbers on one another's chests and undershirts in case they were killed.
Tawfik Dessouki, a Brotherhood supporter, said he was fighting for "democracy" and against the military's ouster of Morsi.
"I am here for the blood of the people who died. We didn't have a revolution to go back to a police and military state again and to be killed by the state," he said during a march headed toward Ramses Square.
At least 12 people were killed near the square as some in the crowd tried to attack a police station, security officials said.
The Facebook page of the army spokesman, Col. Mohammed Ali, accused gunmen of firing from the mosque at nearby buildings. The upper floors of a commercial building towering over Ramses Square caught fire during the mayhem, with flames engulfing it for hours.
Similar battles played out in cities across the country, where people brandishing weapons attacked police and residents fired at one another.
Gunmen targeted police checkpoints and at least 10 police stations came under attack. Egypt's security forces were rocked by the country's 2011 uprising that toppled Mubarak and have not fully recovered since.
In the Red Sea city of Suez, 14 people were killed in clashes between protesters and security forces. In Egypt's second-largest city of Alexandria on the Mediterranean, 10 people were killed during clashes between the two rival camps. Security officials said violence was also fierce in the province of Fayoum, an oasis region southwest of Cairo, where seven people were killed during an attempt to storm the main security building there, a security official said. Two policemen died in the attack.
In the province of Minya south of Cairo, protesters attacked two Christian churches, security officials said. At churches across the country, residents formed human chains to try to protect them from further assaults, and a civilian was killed while trying to protect a church in Sohag, south of Cairo, authorities said.
Many of Morsi's supporters have criticized Egypt's Christian minority for largely supporting the military's decision to remove him from office, and dozens of churches have been attacked this week. The coup that ousted Morsi followed days of protests by millions of Egyptians demanding the Islamist leader step down.
Mourad Ali, a spokesman for the Brotherhood, denounced the attacks on churches, saying they ran counter to Islamic principles and were an attempt to ignite sectarian divisions.
"Our stance is clear. ... We strongly condemn any attack even verbal on churches and on Coptic property. This holds true whether or not Coptic leaders joined in or supported the July 3 coup. ... This does not justify any attack on them," he said in an online statement.