The planned demonstrations, which could plunge Egypt once again into a dangerous round of civil unrest, reflect the growing polarization of the nation since Morsi took power, with the president and his Islamist allies in one camp and seculars, liberals, moderate Muslims and Christians on the other.
Already, clashes across a string of cities north of Cairo over the past week have left at least seven people dead, including an American, and hundreds injured, and there are deep-rooted fears in the country that Sunday's protests will turn violent and quickly spiral out of control.
On Saturday, an Associated Press reporter saw Morsi supporters at a Cairo sit-in doing military-style fitness drills, with some wearing homemade body armor and construction helmets and carrying sticks. They said they had no intention of attacking opposition protesters, and would only act in self-defense or to protect the presidential palace.
The Tamarod, or Rebel, youth movement says its petition is evidence of the widespread dissatisfaction with Morsi's administration, and has used the signature drive as the focal point of its call for millions of people to take to the streets Sunday to demand the president's ouster.
Mahmoud Badr, a Tamarod leader, told reporters Saturday a total of 22,134,460 Egyptians have signed the petition. He did not say whether there had been an independent audit of the signatures.
Morsi's supporters, who have long doubted the validity and authenticity of the collected signatures, expressed skepticism about the final count.
"How do we trust the petitions?" asked Brotherhood member Ahmed Seif Islam Hassan al-Banna. "Who guarantees that those who signed were not paid to sign?"
If authenticated, the collection of so many signatures would deal a symbolic blow to Morsi's mandate and put in stark terms the popular frustrations with an administration that critics say has failed to effectively deal with the country's pressing problems, including tenuous security, inflation, power cuts and high unemployment.
Tamarod, which began its campaign with the goal of collecting more signatures than the 13 million votes Morsi garnered in his 2012 election win, announced its final tally the day before protests that organizers vow will bring millions into the streets to push the president from power.
Morsi, meanwhile, sought to project a business-as-usual image Saturday, meeting with the defense and interior ministers to review preparations to protect the protesters and vital state facilities during Sunday's demonstrations.
Egypt has been roiled by political unrest in the two years since the uprising that ousted autocrat Hosni Mubarak, but the round of protests set to kick off Sunday promises to be the largest and holds the potential to be the bloodiest yet.
In the past week alone, at least seven people have been killed in clashes between the president's supporters and opponents in cities in the Nile Delta, while on Friday protesters ransacked and torched as least five Brotherhood offices across the country.
Adding to the tension, eight lawmakers from the country's interim legislature announced their resignation Saturday to protest Morsi's policies. The 270-seat chamber was elected early last year by less than 10 percent of Egypt's eligible voters, and is dominated by Islamists who support Morsi.
With a sense of doom hanging over the country, Defense Minister Gen. Abdel-Fattah el-Sissi last Sunday gave the president and his opponents a week to reach a compromise and warned that the military would intervene to prevent the nation from entering a "dark tunnel." It was the strongest expression of the military's discontent with conditions in the nation since Morsi took office a year ago.
In South Africa, President Barack Obama said the U.S. supports freedom of speech in Egypt and the right of protesters to peacefully assemble, and called on called on both sides in Egypt to avoid violence.
"We would urge all parties to make sure they're not engaging in violence (and) police and military are showing appropriate restraint," he said.
The opposition, feeling that Morsi may be on the ropes and frustrated by past offers of dialogue that proved to be mostly symbolic, has shown no inclination to compromise, and Morsi offered no concessions to his opponents when he addressed the nation for 2 ½ hours on Wednesday.
The focus of Sunday's protests is Morsi's Ittihadiya palace in Cairo. As a precaution, the president and his family are reported to have moved into the Cairo headquarters of the Republican Guard, the branch of the army tasked with protecting the president and presidential palaces.
As the country waits to see what transpires Sunday, thousands of supporters and opponents of the embattled president held rival sit-ins Saturday in separate parts of the capital.
With expectations of violence running high, the military has dispatched troops backed by armored personnel carriers to reinforce military bases on the outskirts of cities expected to be flashpoints.
In Cairo, the additional forces were deployed to military facilities in the suburbs and outlying districts. Army troops are also moving to reinforce police guarding the city's prisons to prevent a repeat of the nearly half dozen jail breaks during the chaos of the 2011 uprising.
The opposition is demanding Morsi's ouster, saying he has lost his legitimacy through a series of missteps and authoritarian policies. They say early presidential elections should be held within six months of his ouster.
Hard-line Islamists loyal to Morsi have repeatedly vowed to "smash" the protesters, arguing that they were a front for loyalists of Hosni Mubarak, the autocrat ousted in Egypt's 2011 revolt, determined to undermine Morsi's rule. They also say that Morsi is a freely elected president who must serve out his four-year term before he can be replaced in an election.
Many Egyptians fear the new round of unrest could trigger a collapse in law and order similar to the one that occurred during the 2011 revolt. Already, residents in some of the residential compounds and neighborhoods to the west of the city are reporting gunmen showing up to demand protection money or risk being robbed.
The police, who have yet to fully take back the streets after they disappeared in unclear circumstances in 2011, have stepped up patrols on the outskirts of the city, ostensibly to prevent weapons and ammunition from coming into the city to be used in the case of an outbreak of violence. The army is advertising hotlines for civilians to call if they run into trouble.
In the latest reminder of the near lawlessness that has plagued the Sinai Peninsula bordering Gaza and Israel since the 2011 revolt, a senior security official officer was assassinated Saturday in the coastal city of el-Arish as he arrived home from work. Police Brig. Mohammed Tolbah was instantly killed and his driver seriously injured.
___
Associated Press writer Maggie Michael contributed to this report.