CAIRO — 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 clashed with 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 in clashes that killed more than 600 people.
Military helicopters circled overhead as residents furious with the Brotherhood protests pelted them with rocks and glass bottles. The two sides also fired on one another, sparking running street battles throughout the capital’s residential neighborhoods.
There was little hope that an evening curfew would end the violence as the Muslim Brotherhood called on supporters of the country’s ousted Islamist president, Mohammed Morsi, to stage daily protests.
Unlike in past clashes between protesters and police, residents and possibly police in civilian clothing battled those participating in the Brotherhood-led marches. There were few police in uniform to be 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.
Across the country, at least 72 civilians were killed, along with 10 police officers, security officials said. They spoke on condition of anonymity in line with regulations.
The violence erupted shortly after Friday prayers, which had been the launching point of many protests at the beginning of the Arab Spring. 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 checkpoint, residents barred ambulances and cars carrying wounded from Cairo’s main battleground, Ramses Square, from reaching a hospital.
The scenes highlighted how dangerous the divisions in Egypt have become. At least nine police stations were attacked Friday, officials said. On Thursday, the Interior Ministry said it had authorized the use of deadly force against anyone targeting police and state institutions. But the threat appeared not to intimidate protesters.
The Brotherhood-led marches in Cairo headed toward Ramses Square, near the country’s main train station. The area is near Tahrir Square, where the army put up barbed wire and deployed 30 tanks outside the Cairo Museum overlooking the square as a buffer between the protesters and a small anti-Brotherhood encampment in the square.
The square was the site of massive 2011 protests that led to the ouster of longtime president Hosni Mubarak.
Several of the protesters were seen writing their names and relatives’ phone numbers on one another’s chests and undershirts in case they were to die in Friday’s clashes.
Tawfik Dessouki, a Brotherhood supporter, said he was ready to fight 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 after police fired on protesters. Some appeared to be trying to attack a nearby 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.
Associated Press photographers saw many of the dead inside the mosque-turned-morgue, which was also acting 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 upper floors of a commercial building towering over Ramses Square caught fire later in the day, with flames engulfing it for hours. It was not immediately clear what caused the fire at the building housing the Arab Contractors’ construction company, but no injuries were reported.
In the canal city of Suez, 14 people were killed in clashes between protesters and security forces. In Egypt’s second-largest city of Alexandria, 10 people were killed during clashes between the two rival camps. Security officials said violence was also fierce in the province of Fayoum, just west 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 southern province of Minya, two churches were attacked by protesters, security officials said. At churches across the country, residents formed human chains 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 voiced criticism at Egypt’s Christian minority for largely supporting the military’s decision to oust him from office, and dozens of churches have been attacked this week.
Egypt, the Arab world’s most populous nation, has been in turmoil since Morsi was removed from power by the military on July 3, following days of mass protests against him and his Brotherhood group. But Morsi’s supporters have remained defiant, demanding the coup be overturned. The international community has urged both sides to show restraint and end the turmoil engulfing the nation.