CAIRO (AP) -- Egypt's capital descended into chaos Friday as vigilantes at neighborhood checkpoints battled Muslim Brotherhood-led protesters denouncing the ouster of President Mohammed Morsi and a deadly crackdown. The fiercest street clashes Cairo has seen in more than two years of turmoil left at least 82 people dead, including 10 policemen.
The sight of residents firing at one another marked a dark turn in the conflict, as civilians armed with pistols and assault rifles fought protesters taking part in what the Muslim Brotherhood called a "Day of Rage" -- ignited by anger at security forces for clearing two sit-in demonstrations Wednesday that sparked nationwide clashes in which more than 600 people died.
Military helicopters circled overhead 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.
Across the country, at least 72 civilians were killed, along with 10 police officers, security officials said, speaking on condition of anonymity in line with regulations.
Friday's violence capped off a week that saw more than 700 people killed across the country -- surpassing the combined death toll from two and a half years of violent protests since the ouster of longtime leader Hosni Mubarak until the toppling of Morsi in a July 3 coup.
Unlike in past clashes between protesters and police, Friday's violence introduced a combustible new mix, with residents and police in civilian clothing battling those participating in the Brotherhood-led marches.
Few police in uniform were seen as neighborhood watchdogs 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 ambassadors reside.
Friday's violence erupted shortly after midday prayers when tens of thousands of Brotherhood supporters answered the group's call to protest across Egypt in defiance of a military-imposed state of emergency following the bloodshed earlier this week.
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 Cairo's main battleground, Ramses Square, from reaching a hospital.
By choosing Ramses Square as the focus of Friday's demonstrations, the Brotherhood appeared to be trying to establish another protest site to replace the two forcibly cleared Wednesday -- but this time in an area that cuts through the heart of Cairo. The area is near Tahrir Square, where the army put up barbed wire and deployed 30 tanks outside the Egyptian Museum overlooking the area as a buffer between the protesters and a small anti-Brotherhood encampment in the square.
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 in Friday's clashes.
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.
Heavy gunfire rang out over a main overpass where pro-Morsi protesters were marching toward Ramses Square. Video online showed protesters trying to flee the bullets, with at least one person jumping off the high overpass and others hanging off the side. Some used a rope to get down. It was not immediately clear where the bullets were being shot from.
Alia Mostafa of the Anti-coup Alliance, a group that works closely with the Brotherhood, said snipers were shooting down at protesters in the Ramses Square area.
"Police are firing live ammunition from the roof tops of the nearby police station," she said.
At least 12 people were killed near the square as some in the crowd tried to attack a police station, security officials said. Inside Al-Fath mosque near Ramses Square, where the Brotherhood urged its Cairo supporters to converge, blood-soaked bodies with bullets to the head and chest lay next to one another.
The mosque-turned-morgue was also being used as a field hospital where the wounded were being wheeled in on wooden crates. One corpse had a name and phone number scribbled on the chest.
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.