That schism grew after President Mohammed Morsi, Egypt's first democratically elected leader, was ousted in a July 3 military coup. But it was Wednesday's deadly police raids with armored bulldozers and security forces plowing through two protest camps that will be remembered as a turning point when what had been primarily a political standoff erupted into bloodshed.
"The spark of civil war is out," wrote Islamist columnist and author Fahmy Howeidy in Thursday's edition of the independent al-Shorouk daily. "The nation is on the edge of an abyss."
Adding to the mix is the branding by the state media of Morsi's Muslim Brotherhood and allies as "terrorists" and growing calls for authorities to take a tougher approach on the Islamists.
In a glimpse of what may be in store for the most populous Arab state, dozens of revenge attacks and clashes spilled over into a second day Thursday in Cairo and other cities showing the capability of Islamists to strike and laying bare the depth of their anger over Morsi's ouster and the crackdown that left hundreds dead.
Angry young men attacked government and security buildings, setting some ablaze, cut off roads, damaged or torched dozens of churches and stormed more than 20 police stations.
In one particularly gruesome attack, four officers in a police station just outside Cairo were killed after the building was shelled with rocket-propelled grenades. The assailants then slit the police chief's throat, a brutality reminiscent of an Islamist, anti-government insurgency that raged in Egypt in the 1990s before Mubarak used force to suppress it, killing and jailing thousands of Islamists.
In response, the government authorized police Thursday to use deadly force against anyone attacking security forces or government installations.
While the international community largely condemned the overwhelming use of force to clear out the camps on Wednesday, the military-backed administration's fight against the Brotherhood so far has been supported by many Egyptians, who are mainly Muslim but object to hard-liners.
"The army and the police will strike hard and ordinary people will be supportive," prominent rights lawyer and activist Gamal Eid said.
To such observers, it is beyond doubt that a majority of Egyptians supports going after the Brotherhood and its hard-line allies.
Millions took to the streets for days prior to the July 3 coup to call on Morsi to step down, angry over what they saw as efforts to monopolize power for himself and the Brotherhood, failure to implement crucial social and economic reforms and his public quarrels with the judiciary, the media, the military and police.
The mass protests morphed into celebrations on the day of his ouster. And a similar number responded to a call by military chief Gen. Abdel-Fattah el-Sissi to take to the streets on July 26 to show support for his moves to tackle "violence and potential terrorism."
The military and police also have gone after the Muslim Brotherhood and like-minded groups on the legal front, arresting dozens including senior leaders.
State-run TV and newspapers, meanwhile, are filled with commentators and other content full of anti-Brotherhood sentiment, often portraying Islamists as enemies of the people and tapping into nationalistic fervor by alleging that the Brotherhood is a violent group that is secretly enlisting foreign help against the rest of Egyptians and that views Egypt as just a part in a greater Muslim nation that transcends borders.
A backlash against Mohammed ElBaradei's decision to resign as interim vice president to protest the violence illustrated how widespread is the antipathy to the Brotherhood and its allies. The Nobel Peace Prize laureate and former director of the U.N. nuclear agency said he quit because he did not want to be held responsible for bloodshed.
"It has become difficult for me to continue to take responsibility for decisions I disapprove of, and I fear their consequences," he said in his letter of resignation. "I regret that those who benefited today are the proponents of violence, terror and the more extreme groups, and you will remember my words to you."
His resignation earned him public rebuke from Tamarod, the youth group that engineered the mass protests preceding Morsi's ouster. It said he was dodging his responsibility at a time when his services were needed. Even the umbrella of opposition groups he led during Morsi's year in power regretted his decision and bemoaned that he did not bother to consult it beforehand.
A front-page editorial in the state-owned al-Akhbar daily on Thursday said ElBaradei's resignation "amounts to a breach of his position and, consequently, is a case of treason that should not be allowed to pass without accountability."
In anticipation of mass protests by Brotherhood supporters on Friday, Tamarod, or Rebel, has called on Egyptians to form popular committees to counter any violence by the Islamists during the demonstrations, proposing a scenario that places rivals face to face on the streets with a chance of violence breaking out.
Already, Islamist hard-liners in the strategic Sinai Peninsula are waging a worsening insurgency against security forces, with near daily attacks. Sinai has for several years now been roiled in unrest, but the dramatic increase in the number of attacks on security forces there began as soon as Morsi was ousted, leading many to deduce that the Brotherhood and militants in Sinai were somehow bonded.
"Sure civil war is a possibility," said Michael W. Hanna, an expert on Egypt from the New York-based Century Foundation. "It will be bad, with suicide bombings and assassinations but not necessarily another Syria or Iraq."
Hendawi is chief of bureau for The Associated Press in Cairo. He has covered the Middle East for the AP since 1995.