A standoff at the al-Fath mosque continued for most of the day, with exchanges of gunfire between security forces and supporters of deposed President Mohamed Mursi and the Muslim Brotherhood.
The latest violence followed Friday's bloodletting, in which 173 people died across the crisis-wracked Arab country. At least 800 people have been killed in three days of fighting after security forces broke up Brotherhood protest camps in Cairo early last week. Yesterday, it was confirmed that a son of Mohammed Badie, the Muslim Brotherhood's spiritual leader, was one of those killed.
Yesterday's clashes also came as Egypt's interim Prime Minister, Hazem Beblawi, proposed legally dissolving the Brotherhood, a move sure to further inflame a situation that many fear could tip Egypt into civil war. Spokesman Sherif Shawki said prime minister Beblawi assigned the ministry of social solidarity to study the legal possibilities of dissolving the group. He did not elaborate.
The Muslim Brotherhood group, founded in 1928, came to power a year ago when its leader Mohamed Mursi was elected in the country's first free presidential elections. The polls came after the overthrow of long-time autocratic president Hosni Mubarak. Mursi was overthrown in a popularly backed military coup July 3.
At the al-Fath mosque in Cairo's central Ramses Square, where Brotherhood members had barricaded themselves inside, gunmen opened fire on security forces from a second-floor window.
Hundreds of Mursi supporters have been taking refuge inside the mosque, which has been used as a makeshift field hospital since protests turned violent on Friday.
The Muslim Brotherhood has said it is committed to peaceful resistance to the army-backed government that toppled Mursi. But a Brotherhood spokesman last week said anger was out of control because of the army's security crackdown.
Yesterday tensions started to run high when a woman wearing a niqab - the full head-to-toe black veil - tried to walk out of the mosque. A group of about 10 soldiers had been telling people to leave the mosque and that they would be in no danger.
When the woman approached them, people in the mosque could be overheard saying she was the wife of a Brotherhood leader and was in danger of being arrested. She walked back into the mosque, looked up and said something to a group of pro-Mursi gunmen armed with Kalashnikov assault rifles.
It was then, according to witnesses, that the shooting started. Very quickly the scene became chaotic, with teargas fired into the building and live ammunition fired by both sides. Soldiers and civilians took cover behind sand-coloured armoured personnel carriers positioned strategically in the street outside. Al-Jazeera television called one woman inside the mosque on her mobile phone as the shooting began.
"Nobody here is safe, they are shooting inside the mosque," she said, with the sound of loud firing heard in the background.
When the mosque was finally cleared, Egyptian police began bringing some Mursi supporters out of the building, leading some, dragging others but then having to protect them from angry anti-Brotherhood mobs armed with bats and pieces of wood who tried to attack them.
Elsewhere, in a day of renewed tension, Egyptian authorities said they had arrested the brother of al-Qaeda chief Ayman al-Zawahiri.
Mohammed al-Zawahiri was detained at a checkpoint in Giza, near Cairo, because of his links to Mursi, according to security officials.
In another Egypt-related development yesterday, a bomb blast ripped through the garden wall of the Egyptian consulate in the eastern Libyan city of Benghazi, injuring a security guard who needed hospital treatment.
At least five children were also cut by flying glass from the explosion, which blew out windows and significantly damaged a building opposite the consulate.
Across Egypt, the Muslim Brotherhood has vowed to continue its "days of rage" and keep up the protests, leaving Egypt bracing itself for yet more violence to come.