An unexpected twist came when the defense minister, a Morsi appointee, invited the opposition, along with judges, media leaders and Muslim and Christian clerics to an informal gathering Wednesday, saying he was doing so in his personal not an official capacity.
It was the second time this week that the nation's powerful military has addressed the crisis, signaling its return to the political fray after handing over power in June to Morsi, Egypt's first civilian president.
The military sees itself as the guarantor of Egypt's interests and secular traditions. Earlier this week, it warned of disastrous consequences if the crisis over the country's draft constitution is not resolved.
"We will only sit together ... For the sake of every Egyptian, come and disagree. But we won't be cross with one another or clash," Defense Minister Abdel-Fatah el-Sissi, said on state television.
"We are not concerned with politics. We want to reassure the people that we can sit together," added Maj. Gen. Mohammed el-Assar, el-Sissi's deputy, speaking on a private TV network.
The opposition said it would not participate in any meeting that was nothing more than an informal gathering. The Brotherhood said it would attend.
Egypt's political crisis began on Nov. 22 when Morsi issued a decree granting himself and the Islamist-dominated panel that drafted the constitution immunity from judicial oversight or challenge, sparking mass demonstrations.
The constituent assembly then hurriedly approved the draft constitution in a marathon overnight session, prompting hundreds of thousands of the president's opponents to take to the streets in massive rallies the largest since the uprising that toppled Mubarak in February 2011.
The vast majority of Egypt's judges, meanwhile, said Tuesday they would not oversee the referendum on the draft constitution. Ahmed el-Zind, chairman of the Judges' Club and a fierce Morsi critic, told a news conference that 90 percent of the nation's judges would join the boycott.
The move was unlikely to stop the referendum from taking place, but it cast further doubt on the legitimacy of the constitutional drafting process and, ultimately, the document itself.
Late Tuesday, Morsi issued a decree declaring the vote would be staggered over two days, Dec. 15 and Dec. 22, a move designed to make up for the shortage of judges. A one-time Mubarak supporter, el-Zind has led the judges angered by what they see as Morsi's "assault" on the judiciary.
Zaghloul el-Balshi, head of the referendum's organizing committee, told the private ONTV network that 9,000 judges had agreed to oversee the voting. His claim could not be independently verified.
Prime Minister Hesham Kandil, meanwhile, said Egypt requested a postponement of the $4.8 billion IMF loan after Morsi suspended a package of tax hikes that had been part of a program to reduce Egypt's huge budget deficit.
Although austerity is unavoidable, political tensions have made the suspension of the hikes necessary, Kandil said. The IMF executive board was expected to vote on the deal on Dec. 19.
In Cairo's Nasr City district, a Muslim Brotherhood stronghold, tens of thousands of the president's backers, some waving Egyptian flags, voiced their support for the constitution in a massive rally in front of a local mosque.
"I want the chant of 'Morsi' to shake the Earth!" a man shouted into a microphone. "Alleyway to alleyway, house to house, the constitution means stability."
The crowd grew rapidly as dozens of buses transported thousands of Morsi supporters from provinces outside of Cairo. Many of the men wore beards, a hallmark of Islamists, while the women wore the Muslim veil or the niqab, which covers everything except the eyes.
The crowd denounced the liberal opposition and its leaders, calling them undemocratic and accusing them of being Mubarak loyalists.
"Those protesting at the presidential palace are feloul (remnants of the Mubarak regime) and counter-revolutionaries," said Mohammed Abdel-Aziz, a young Islamist protester. "They don't want Islam."
Another pro-Morsi protester, school teacher Mohammed el-Hamoul, said Islamists "accepted democracy so we could reach power."
"Now those who claim to be democracy advocates lost faith in democracy when the Islamists rose to power," he said.
Several hundred Islamists also have set up camp outside a media complex that is home to several independent TV networks critical of Morsi and the Brotherhood. The Islamists have threatened to storm the facility.
The opposition, meanwhile, staged its rally in the nearby Heliopolis neighborhood, where tens of thousands of protesters gathered outside the presidential palace, pushing their demands that Morsi scrap the referendum.
"The people want the downfall of Brotherhood rule!" the protesters chanted, alluding to the widespread notion that Mohammed Badie, the spiritual leader of the Muslim Brotherhood, is the country's actual ruler.
Troops belonging to the elite Republican Guards deployed outside the palace did not intervene, with some posing for the protesters' cameras.
With four days to go before the referendum, the opposition has yet to decide whether to campaign for a "no" vote or call for a boycott something many see as a reflection of the divisions in the anti-Morsi camp. The disparate opposition groups are led by Nobel Peace Prize laureate Mohamed ElBaradei, Egypt's former foreign minister and Arab League chief Amr Moussa and leftist politician Hamdeen Sabahi.
Cracks in the opposition's unity first appeared last weekend when one of its leading figures, veteran opposition politician Ayman Nour, accepted an invitation by Morsi to attend a "national dialogue" meeting. On Monday, another key opposition figure, El-Sayed Badawi of the Wafd party, met Morsi at the presidential palace.
Badawi later issued a statement saying he remained loyal to the opposition's goals of scrapping the draft charter and postponing the vote.
The opposition has also demanded that Morsi rescind decrees giving him near- absolute powers. He withdrew those powers on Saturday, but insisted that the referendum would go ahead as scheduled.
Anticipating unrest on the days the referendum is held, Morsi has ordered the military to join the police in maintaining security and protecting state institutions until after the results of the vote are announced. The decree went into effect on Monday.