CNN- After a historic revolution that toppled a 30-year regime, Egyptians eagerly waited Sunday to learn who would be the country's first democratically elected president.
Officials braced for violence and the Muslim Brotherhood said it would stage a long-term protest if a former prime minister is declared the winner.
Egypt is set to announce the winner at 3 p.m. (9 a.m. ET) Sunday, according to the Supreme Presidential Elections Commission.
Both candidates have already claimed victory. And hours before the announcement Sunday, both campaigns reiterated the claim.
Former Prime Minister Ahmed Shafik made the declaration on his Facebook page: "President Ahmed Shafik, Egypt 2012."
Mohamed Morsi of the Freedom and Justice Party, the political arm of the Muslim Brotherhood, also declared on Facebook that "at 3:00 p.m., Morsi will be Egypt's president."
The claims come amid heightened concerns that Shafik, who served under ousted leader Hosni Mubarak, would give new life to the old guard and essentially nullify democratic gains since last year's Egyptian revolution.
"Did we really have a revolution if Shafik wins?" prominent novelist Alaa al-Aswany said via Twitter. "For the thousandth time this is not a battle between the military and the (Muslim) Brotherhood, it is a battle of the Egyptian people with the military regime that ruled us with an iron fist for 60 years."
Like Mubarak, Shafik is a former air force officer with close ties to Egypt's powerful military and is "the quintessential candidate of the counter-revolution," said Khaled Elgindy, a visiting fellow at the Brookings Institution in Washington.
Morsi, an American-educated engineer, "represents the older, more conservative wing of the Brotherhood and openly endorses a strict Islamic vision," said Isobel Coleman of the Council on Foreign Relations.
But in an interview with CNN, Morsi said, "There is no such thing called an Islamic democracy. There is democracy only. ... The people are the source of authority."
Each campaign has accused the other of election fraud.
On Saturday, authorities reviewed about 400 electoral violation reports submitted by the two candidates.
A national security officer predicted violence if Shafik is declared the victor.
"In the event of Shafik's win, we expect some trouble on the street and in Tahrir (Square), which will be met with an iron hand according to the instructions we have received," said Lt. Col. Usama Emam, a national security officer.
"We are on high alert and so far there has not been any evidence of an imminent threat or plan of sabotage from any Islamist extremist groups," Emam said. He added that Egyptian authorities have arrested "elements" of the Palestinian group Hamas over the past week since Egypt's military rulers isued "de facto martial law and we are still tracking some of their fugitive members who had entered mainly through Sinai and made their way to Cairo."
More than 1,800 ambulances have been dispatched across the country as a proactive measure, the state-run EgyNews agency reported. It also said the country's interior ministry stressed the need to respect peaceful demonstrations.
But the ministry also said it would not tolerate any turmoil against authorities after Sunday's pivotal announcement.
"Minister Mohamed Ibrahim has given police forces orders to shoot to kill against anyone attempting to attack police stations after the results," interior ministry spokesman Gen. Marwan Mustapha said, reiterating government policy in such circumstances. "Increased security has been dispersed in the side streets of (Cairo's) Tahrir Square to protect government buildings."
If Shafik wins the election, the Muslim Brotherhood will stage "a long-term, open-end sit-in at Tahrir Square," complete with bathroom facilities made of bricks, daily food supply and tight security at the entrances of the square, said Jihad Haddad, a political adviser to the Muslim Brotherhood. Haddad cited the Brotherhood's disapproval of the ruling military body's new constitutional decree and de facto martial law.
Egypt's all-powerful military leaders have said they won't reverse their widely deplored constitutional and judicial changes and also cautioned against election-related unrest.
"We will face anyone who will pose a challenge to the public and private sectors with an iron fist," the Supreme Council of the Armed Forces (SCAF) said.
Egypt's constitutional court dissolved the lower house of parliament this month, extending the military's power and sparking accusations of a coup d'etat.
Adding to the electoral tension is the question of how much power the new president will actually wield now that the military council has full legislative authority.
Under an interim constitutional declaration, the military council retains the power to make laws and budget decisions until a new constitution is written and a new parliament elected.
The declaration said Supreme Council members "shall decide all matters related to military affairs, including the appointment of its leaders." The president has the power to declare war, it says, but only "after the approval" of the Supreme Council.
The military council said it does not favor one political entity over another and respects the rights of Egyptians to protest but stressed the importance of self-restraint and respect for authority.
The Supreme Council urged political entities to respect democracy and "abstain from all possible acts that may descend the country into a full chaos."
Egyptian reform leader Mohamed ElBaradei -- the former head of the United Nations nuclear watchdog agency and a Nobel Peace Prize laureate -- said that if Shafik is declared the winner, "we are in for a lot of instability and violence ... a major uprising."
He said he isn't as worried about a Morsi victory because Shafik supporters are unlikely to take their anger to the streets.
ElBaradei described the current situation as "a total, complete 100% mess."
Mohamed Mahsoob, a law professor at Menofiya University and a member of the El Wasat Party, tweeted: "The revolution will succeed, even if the newly elected president is below expectations because we will have the right to change him. But the revolution will not succeed if we have a president from the old regime that we toppled because he will working on seizing it back (and) reversing the accomplishments."
Amr Moussa, who served as foreign minister under Mubarak and mounted an effort to win the presidency in these elections, said "the next Egyptian president must call upon everyone to stand united as one." According to state-run news agency MENA, Moussa called on the new president "to head an emergency government of technocrats" that would last six to 12 months.