Story highlights Residents, Mohamed Morsy backers clash in Helwan, south of Cairo, state TV says

Neither the government or Morsy supporters give any indication of backing down

An official says 72 pro-Morsy protesters in Nasr City are killed

Government officials say police didn't open fire; the opposition says authorities did

All agree that scores angry at Egypt's military-backed government and the ouster of President Mohamed Morsy died in late-night clashes in the volatile nation's capital.

But they are of opposite minds as to who began firing first and who is to blame.

Dr. Mohammed Ali Sultan, chairman of Egypt's ambulance services, told CNN that 72 had been killed in Nasr City, an area of Cairo the Muslim Brotherhood has made its base after the group's former leader was forced from power and ordered jailed.

Medics in a Brotherhood field hospital there earlier Saturday had put the death toll at 66, with another 61 on life support and thousands more wounded.

How did they end up in such straits?

Ask the Muslim Brotherhood -- the Islamist group that was sidelined under longtime Egyptian leader Hosni Mubarak only to become the country's dominant political force after his forced exit in 2011 -- and its members will say police fired live ammunition on protesters Friday and Saturday.

A wounded protester getting medical treatment at a field hospital said he saw men in plainclothes fire on pro-Morsy demonstrators with shotguns.

Photos: 2013 unrest in Egypt Photos: 2013 unrest in Egypt Unrest in Egypt – A bus passes a destroyed pickup truck with loudspeakers that was used by supporters of ousted Egyptian President Mohamed Morsy on Friday, August 2. The supporters and security forces clashed in Sixth of October City in Giza, south of Cairo, after the government ordered their protest camps be broken up. Look at the latest violence in Egypt. Hide Caption 1 of 83 Photos: 2013 unrest in Egypt Unrest in Egypt – Morsy supporters walk past makeshift roadblocks at Rabaa al-Adawiya Square in Cairo on Saturday, August 3. Security forces set up the roadblocks outside the square, allowing people to leave but not enter, as they attempt to break up camps set up during ongoing protests over Morsy's ouster. Hide Caption 2 of 83 Photos: 2013 unrest in Egypt Unrest in Egypt – Morsy supporters run among the smoke and fire resulting from clashes with security forces in Sixth of October City in Giza on August 2. The military ousted Morsy, Egypt's first democratically elected president, in early July after days of mass demonstrations. Dozens of Morsy backers angry at Egypt's military-backed government have died in weekend violence in the volatile nation's capital. See photos of protests that have engulfed the country. Hide Caption 3 of 83 Photos: 2013 unrest in Egypt Unrest in Egypt – Egyptian riot police block the entrance to Sixth of October City in Giza on August 2 following clashes with Morsy supporters. Hide Caption 4 of 83 Photos: 2013 unrest in Egypt Unrest in Egypt – Morsy supporters in red helmets march during a protest against the government in Cairo on August 2. Pro-Morsy marches began after Friday prayers, when supporters made their way back to their camp outside the Rabaa al-Adawiya mosque. Hide Caption 5 of 83 Photos: 2013 unrest in Egypt Unrest in Egypt – Morsy supporters march in a demonstration against the Egyptian government in Cairo on August 2. Hide Caption 6 of 83 Photos: 2013 unrest in Egypt Unrest in Egypt – Supporters of Egypt's deposed President Mohammed Morsy gather for prayers at Nasr City, where protesters have installed a camp and hold daily rallies, in Cairo, on Sunday, July 28. Hide Caption 7 of 83 Photos: 2013 unrest in Egypt Unrest in Egypt – A boy wears a tear gas mask as supporters of Egypt's ousted President Mohammed Morsy pray at the camp set up by supporters in the Nasr City area of Cairo on July 28. Hide Caption 8 of 83 Photos: 2013 unrest in Egypt Unrest in Egypt – Doctors treat an injured supporter of deposed Egyptian President Mohamed Morsy during clashes with security forces in Cairo on Saturday, July 27. Hide Caption 9 of 83 Photos: 2013 unrest in Egypt Unrest in Egypt – A wounded Morsy supporter lies on the floor of a field hospital in Cairo on July 27. Thousands of Morsy supporters gathered Saturday in the Nasr City neighborhood despite dozens of deaths the night before and veiled threats from the military. Hide Caption 10 of 83 Photos: 2013 unrest in Egypt Unrest in Egypt – Supporters of Morsy protest outside a field hospital in Cairo where the bodies of slain Morsy supporters have been brought July 27. Hide Caption 11 of 83 Photos: 2013 unrest in Egypt Unrest in Egypt – The body of a Muslim Brotherhood protester, reportedly shot dead after violence erupted the night before, is moved as mourners watch inside a field hospital in Cairo on July 27. Hide Caption 12 of 83 Photos: 2013 unrest in Egypt Unrest in Egypt – Two men mourn Morsy supporters who were killed in overnight clashes with security forces, in Cairo, on July 27. Hide Caption 13 of 83 Photos: 2013 unrest in Egypt Unrest in Egypt – A medic pauses at a field hospital in Cairo on July 27 after tending to the bodies of Morsy supporters reportedly killed in fighting. Hide Caption 14 of 83 Photos: 2013 unrest in Egypt Unrest in Egypt – Supporters of Morsy carry an injured man to a field hospital amid clashes with security forces in Cairo on July 27. Hide Caption 15 of 83 Photos: 2013 unrest in Egypt Unrest in Egypt – Doctors treat a Morsy supporter injured during clashes with security forces in Cairo on July 27. Hide Caption 16 of 83 Photos: 2013 unrest in Egypt Unrest in Egypt – Supporters of Morsy rally in Giza, on Friday, July 26. Hide Caption 17 of 83 Photos: 2013 unrest in Egypt Unrest in Egypt – Supporters of the Egyptian military rally at Tahrir Square in Cairo on Friday, July 26. Hide Caption 18 of 83 Photos: 2013 unrest in Egypt Unrest in Egypt – Morsy opponents rally in Cairo on July 26. Hide Caption 19 of 83 Photos: 2013 unrest in Egypt Unrest in Egypt – Morsy opponents watch a demonstration from a rooftop near Tahrir Square in Cairo on July 26. Hide Caption 20 of 83 Photos: 2013 unrest in Egypt Unrest in Egypt – Egyptian soldiers stand guard atop an armored vehicle on a bridge leading to Cairo's Tahrir Square on Friday, July 26. Hide Caption 21 of 83 Photos: 2013 unrest in Egypt Unrest in Egypt – A Morsy advocate builds a giant portrait of the deposed president Thursday, July 25, while other supporters hold a sit-in outside a Cairo mosque. The military has detained Morsy while an interim government takes shape. Hide Caption 22 of 83 Photos: 2013 unrest in Egypt Unrest in Egypt – Morsy supporters say evening prayers during a rally July 25 outside a Cairo mosque. Hide Caption 23 of 83 Photos: 2013 unrest in Egypt Unrest in Egypt – A man with a pistol and other Morsy opponents detain a suspected Morsy supporter who was wounded during clashes in Cairo on Monday, July 22. Supporters and opponents clashed near the city's Tahrir Square. Hide Caption 24 of 83 Photos: 2013 unrest in Egypt Unrest in Egypt – Men evacuate an injured opponent of Morsy during clashes with his supporters in Cairo on July 22. Hide Caption 25 of 83 Photos: 2013 unrest in Egypt Unrest in Egypt – A man fires a gun during clashes between opponents and supporters of Morsy in Cairo on July 22. Hide Caption 26 of 83 Photos: 2013 unrest in Egypt Unrest in Egypt – A riot police officer aims rubber bullets toward Morsy supporters in Cairo on July 22. Hide Caption 27 of 83 Photos: 2013 unrest in Egypt Unrest in Egypt – Riot police evacuate an injured anti-Morsy protester in Cairo on July 22. Hide Caption 28 of 83 Photos: 2013 unrest in Egypt Unrest in Egypt – A Morsy supporter, center, who was allegedly beaten by opponents of Morsy runs during clashes in Cairo on July 22. Hide Caption 29 of 83 Photos: 2013 unrest in Egypt Unrest in Egypt – A Morsy opponent carries his injured friend in Cairo on July 22. Hide Caption 30 of 83 Photos: 2013 unrest in Egypt Photos: Unrest in Egypt – Supporters of Morsy pause for Friday prayers on July 19 at Nasr City in Cairo, where protesters have installed their camp and held daily rallies. Hide Caption 31 of 83 Photos: 2013 unrest in Egypt Photos: Unrest in Egypt – Morsy supporters take part in a protest march near government ministry buildings on Wednesday, July 17, in Cairo. Hide Caption 32 of 83 Photos: 2013 unrest in Egypt Photos: Unrest in Egypt – A Morsy supporter is held back by riot police during a rally near Tahrir Square on July 17. Hide Caption 33 of 83 Photos: 2013 unrest in Egypt Unrest in Egypt – A supporter of the Muslim Brotherhood and of Morsy covers his mouth under the 6th October Bridge in Cairo on Tuesday, July 16. Hide Caption 34 of 83 Photos: 2013 unrest in Egypt Unrest in Egypt – A riot police officer fires tear gas toward Morsy supporters during clashes in Cairo on Monday, July 15. Hide Caption 35 of 83 Photos: 2013 unrest in Egypt Unrest in Egypt – Morsy supporters run from tear gas in Cairo on July 15. Hide Caption 36 of 83 Photos: 2013 unrest in Egypt Unrest in Egypt – Egyptians in Cairo's Tahrir Square pray before breaking their fast on the third day of Ramadan, the sacred holy month for Muslims, on Friday, July 12. Hide Caption 37 of 83 Photos: 2013 unrest in Egypt Unrest in Egypt – Supporters of the deposed Morsy rally in Nasr City, Egypt, a suburb of Cairo, on Monday, July 8. Hide Caption 38 of 83 Photos: 2013 unrest in Egypt Unrest in Egypt – A man reacts after seeing the body of a family member at the Liltaqmeen al-Sahy Hospital in Cairo, allegedly killed during a sit-in supporting Morsy in front of the Republican Guard headquarters on July 8. Hide Caption 39 of 83 Photos: 2013 unrest in Egypt Unrest in Egypt – Injured men receive medical attention after clashes between supporters of Morsy and security forces in Cairo on July 8. Hide Caption 40 of 83 Photos: 2013 unrest in Egypt Unrest in Egypt – Opponents of Mohamed Morsy gather at Tahrir Square during a protest in Cairo on Sunday, July 7. Hide Caption 41 of 83 Photos: 2013 unrest in Egypt Unrest in Egypt – Supporters of Morsy pray next to the headquarters of the Republican Guards in Cairo on Saturday, July 6, during the funeral of seven people killed during clashes. Hide Caption 42 of 83 Photos: 2013 unrest in Egypt Unrest in Egypt – People carry coffins on July 6 of two Morsy opponents who were killed during clashes in Cairo. Hide Caption 43 of 83 Photos: 2013 unrest in Egypt Unrest in Egypt – A Morsy supporter joins protests near the University of Cairo in Giza on July 6. Hide Caption 44 of 83 Photos: 2013 unrest in Egypt Unrest in Egypt – Supporters and opponents of Morsy clash in Cairo on Friday, July 5. Hide Caption 45 of 83 Photos: 2013 unrest in Egypt Unrest in Egypt – A protester is attended to in Cairo's Tahrir Square during fighting between the pro- and anti-Morsy crowds on July 5. Hide Caption 46 of 83 Photos: 2013 unrest in Egypt Unrest in Egypt – An Egyptian military helicopter hovers over supporters of the Muslim Brotherhood and deposed President Mohamed Morsy in Cairo on July 5. Hide Caption 47 of 83 Photos: 2013 unrest in Egypt Unrest in Egypt – Morsy supporters hold up their bloodstained hands after Egypt's armed forces opened fire on rally in front of the Republican Guard headquarters in Cairo on July 5. Hide Caption 48 of 83 Photos: 2013 unrest in Egypt Unrest in Egypt – Morsy supporters carry a man who was shot during clashes next to the Republican Guard headquarters in Cairo on July 5. State broadcaster Nile TV said a number of those backing the deposed leader were wounded as they tried to storm the headquarters, where Morsy reportedly was being held. Hide Caption 49 of 83 Photos: 2013 unrest in Egypt Unrest in Egypt – A wounded man is helped following the gun battle outside the headquarters of the Republican Guard on July 5. Hide Caption 50 of 83 Photos: 2013 unrest in Egypt Unrest in Egypt – Egyptians hold portraits of Gen. Abdel-Fatah El-Sisi reading "Come down, Sisi" as they gather in Cairo's landmark Tahrir Square on July 5. Hide Caption 51 of 83 Photos: 2013 unrest in Egypt Unrest in Egypt – Morsy supporters react to an explosion during clashes with police officers on July 5 outside Cairo University in Giza. Hide Caption 52 of 83 Photos: 2013 unrest in Egypt Unrest in Egypt – Egyptian Army soldiers stand guard at the Cairo headquarters of the Republican Guard on July 5 as an Apache attack helicopter flies overhead. Hide Caption 53 of 83 Photos: 2013 unrest in Egypt Unrest in Egypt – Morsy supporters pray near the University of Cairo in Giza on July 5. Hide Caption 54 of 83 Photos: 2013 unrest in Egypt Unrest in Egypt – A man prays on July 5 before the protest near the University of Cairo. Hide Caption 55 of 83 Photos: 2013 unrest in Egypt Unrest in Egypt – Protesters take cover from tear gas during clashes outside the headquarters of the Republican Guard in Cairo on July 5. Hide Caption 56 of 83 Photos: 2013 unrest in Egypt Unrest in Egypt – A military helicopter flies by Egypt's Presidential Palace in Cairo on July 5. Hide Caption 57 of 83 Photos: 2013 unrest in Egypt Unrest in Egypt – Egyptians watch fireworks in Tahrir Square on Thursday, July 4, the day after Morsy's ouster. Hide Caption 58 of 83 Photos: 2013 unrest in Egypt Unrest in Egypt – People dance and cheer in the streets of Cairo on July 4. Hide Caption 59 of 83 Photos: 2013 unrest in Egypt Unrest in Egypt – A Morsy supporter holds a poster of the deposed president during a July 4 rally in Nasr City. Hide Caption 60 of 83 Photos: 2013 unrest in Egypt Unrest in Egypt – A massive crowd gathers in Tahrir Square on July 4. Hide Caption 61 of 83 Photos: 2013 unrest in Egypt Unrest in Egypt – Egyptians cheer and wave national flags as airplanes fly above Tahrir Square on July 4, leaving a trail of smoke in the colors of the national flag. Hide Caption 62 of 83 Photos: 2013 unrest in Egypt Unrest in Egypt – A woman uses a mobile phone to record the July 4 celebrations in Tahrir Square. Hide Caption 63 of 83 Photos: 2013 unrest in Egypt Unrest in Egypt – An opposition protester chants slogans against Morsy near Cairo University, where Muslim Brotherhood supporters gathered on July 4 to show support for the ousted president. Hide Caption 64 of 83 Photos: 2013 unrest in Egypt Unrest in Egypt – A man holds a newspaper near Mesaha Square in Cairo on July 4. Hide Caption 65 of 83 Photos: 2013 unrest in Egypt Unrest in Egypt – Dejected Morsy supporters attend a rally in Nasr City on July 4. Hide Caption 66 of 83 Photos: 2013 unrest in Egypt Unrest in Egypt – A Morsy supporter shows his bloodied shirt during a July 4 rally near the University of Cairo. Hide Caption 67 of 83 Photos: 2013 unrest in Egypt Unrest in Egypt – A young Egyptian boy shoots off fireworks during celebrations in Tahrir Square on July 4. Hide Caption 68 of 83 Photos: 2013 unrest in Egypt Unrest in Egypt – People walk by a pile of Egyptian flags for sale in Tahrir Square on July 4. Hide Caption 69 of 83 Photos: 2013 unrest in Egypt Unrest in Egypt – Crowds throng Tahrir Square on July 4. Hide Caption 70 of 83 Photos: 2013 unrest in Egypt Unrest in Egypt – Egyptian soldiers deploy near Cairo University on July 4. Hide Caption 71 of 83 Photos: 2013 unrest in Egypt Unrest in Egypt – People dance and cheer at Tahrir Square in Cairo on July 4. Hide Caption 72 of 83 Photos: 2013 unrest in Egypt Unrest in Egypt – Adly Mansour, center, stands after delivering a speech during his swearing-in ceremony as Egypt's interim president in the Supreme Constitutional Court in Cairo on July 4. Mansour has served as the head of the country's Supreme Constitutional Court. Hide Caption 73 of 83 Photos: 2013 unrest in Egypt Unrest in Egypt – Armored vehicles with the Egyptian army sit at a checkpoint in the Cairo district of Nasr City on July 4. Hide Caption 74 of 83 Photos: 2013 unrest in Egypt Unrest in Egypt – A Morsy supporter reacts as a military helicopter flies over during a July 4 rally in Nasr City. Hide Caption 75 of 83 Photos: 2013 unrest in Egypt Unrest in Egypt – A boy with face paint the color of the Egyptian flag pauses on July 4 in Tahrir Square. Hide Caption 76 of 83 Photos: 2013 unrest in Egypt Unrest in Egypt – A pedestrian shakes hands with a member of the military at a roadblock in Giza. Hide Caption 77 of 83 Photos: 2013 unrest in Egypt Unrest in Egypt – Security personnel rest on July 4 in Tahrir Square. Hide Caption 78 of 83 Photos: 2013 unrest in Egypt Unrest in Egypt – A man walks to Tahrir Square on July 4. Hide Caption 79 of 83 Photos: 2013 unrest in Egypt Unrest in Egypt – A family sleeps on a bridge near Tahrir Square on July 4. Hide Caption 80 of 83 Photos: 2013 unrest in Egypt Unrest in Egypt – A member of the Egyptian military redirects traffic on July 4 at a roadblock in Giza. Hide Caption 81 of 83 Photos: 2013 unrest in Egypt Unrest in Egypt – Bread is sold near Tahrir Square on July 4. Hide Caption 82 of 83 Photos: 2013 unrest in Egypt Unrest in Egypt – An Egyptian military member guards a roadblock in Giza on July 4. Hide Caption 83 of 83

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He referred to them as "thugs," a term commonly used for young men who support the government and resort to violence.

"Police forces were standing behind them. Also, military forces were outside blocking three entrances to Rabaa Adawiya neighborhood," the protester said, adding he had also seen corpses with gunshot wounds at the hospital.

Yet the prosecutor general's office, according to a report early Sunday on state-run Nile TV, concluded that protesters not only initiated the clashes but also fired live bullets on security forces.

A police spokesman likewise rejected any allegations police opened fire, saying they only used tear gas canisters and were not responsible for the deaths.

Interior Minister Mohamed Ibrahim offered a similar view during a televised news conference.

The protesters were at fault for starting violence that wounded 14 police, none of whom fired back, he said.

"I want to emphasize here that the Interior Ministry police force has never and will never fire its weapons at any Egyptian citizen," Ibrahim said.

Fresh clashes erupted early Sunday in Helwan south of Cairo between residents there and pro-Morsy protesters, reported state TV, citing witnesses.

Meanwhile, an attorney has filed a lawsuit at a district court in Cairo, asking that the military overthrow of Morsy be overturned. Tarek Al Kashef is basing his challenge on the country's constitution, specifically sections that stipulate that a presidential term is four years and that the president is the commander in chief of the armed forces. A hearing is slated for October 8.

Morsy may join Mubarak -- in prison

Morsy has not been seen publicly since the military forced him from office July 3.

The military has not commented on his whereabouts, though a Brotherhood spokesman told CNN he was initially under house arrest at the presidential Republican Guard headquarters in Cairo and later was moved to the Defense Ministry.

Nasser Amin -- a lawyer who met with Morsy's former chief of staff, Refa'a al-Tahtawi, who also is being detained -- told CNN that the former president is being "treated with the utmost respect ... like a statesman."

Yet Amin said that Morsy and others who are being held "can't contact the outside world or lawyers."

The former Muslim Brotherhood leader became Egypt's first democratically president in June 2012 but found himself at odds with the opposition before the military removed him from power and detained him this month.

State media reported he's being held in relation to a jailbreak that took place during Egypt's 2011 revolution but well before he came to power.

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Prosecutors, who ordered a probe two weeks ago, said the escape of Morsy and 18 other Brotherhood members (among others) was plotted by "foreign elements" including Hamas, its military wing, the Islamic Palestinian Army and Hezbollah. The Muslim Brotherhood was named as a domestic group that cooperated with those who broke them out of prison.

Morsy -- who local media reports say was in prison for a single day without any formal charges against him -- is accused of escaping, destroying the prison's official records and intentionally killing and abducting police officers and prisoners.

Now he could be headed back not just to prison, but the same one where Mubarak, the ousted dictator he and his allies have long railed against, is being held.

Ibrahim said Saturday that such a move will probably happen, though an investigative judge will make the final decision on Morsy's next destination.

Government awaits legal OK 'to end the protests'

Neither side gave any hint of backing down -- not just on who's to blame for the latest violence but on the bigger question of whether Morsy should have been deposed and, more recently, ordered jailed over his alleged actions well before he rose to power.

Since Morsy's ouster, supporters of the Muslim Brotherhood and its political arm, the Freedom and Justice Party, have staged mass rallies and sit-ins across the North African nation.

There have been rival rallies as well such as the ones Friday called by military chief Gen. Abdel Fattah al-Sisi to show support for the army's effort to end what he calls "terrorism" -- a statement condemned by the Brotherhood as "inciting violence and hatred."

Mutual trust appears absent as does the prospect of a peaceful resolution anytime soon.

Leaders of the pro-Morsy movement refuse to recognize the interim government or cooperate with it.

The interior minister, meanwhile, had pledged that these rallies will be brought to an end soon.

"We have complete coordination between the police and the armed forces to end the protests at the proper time," Ibrahim said. "... But we are waiting for the prosecutor's office to issue orders so can we have the legal cover for it."

Officials worldwide express concern

Egypt has been on edge since the military forced out Mubarak in early 2011. Yet the situation has clearly gotten more dire in recent weeks.

The European Union's foreign minister condemned the killings of pro-Morsy protesters in Nasr City as well as bellicose language by some Egyptian officials.

"There is no room for hate-speech and other forms of incitement," according to a statement released by Catherine Ashton's office.

U.S. Defense Secretary Chuck Hagel spoke Saturday with al-Sisi, his Egyptian counterpart, to encourage restraint, said Pentagon spokesman George Little.

And U.S. Secretary of State John Kerry talked Saturday with Egypt's interim vice president and its foreign minister to express Washington's deep concern about the bloodshed.

"This is a pivotal moment for Egypt," Kerry said in a statement. "Over two years ago, the revolution began. Its final verdict is not decided, but it will be forever impacted by what happens now."