Supporters of presidential candidate Ahmed Shafik kiss his poster during a protest against the Muslim Brotherhood's presidential candidate Mohamed Morsy in front of the military parade stand at Nasr City in Cairo June 23, 2012. (Amr Abdallah Dalsh/Reuters)

Egyptian election officials said Saturday that they will confirm the results of the nation’s first democratic presidential election on Sunday, an announcement that will either usher in the Arab world’s first Islamist head of state or place at the helm a veteran of deposed leader Hosni Mubarak’s secular government.

The announcement is set to come one week after a run-off vote ended and three days after the elections commission initially pledged to declare the winner, a delay the body said was needed to review hundreds of complaints lodged by the campaigns. Both candidates — the Muslim Brotherhood’s Mohamed Morsi and former prime minister Ahmed Shafiq — have claimed narrow victories.

The announcement would also come more than 17 months after Egyptians began massing in this city’s Tahrir Square in a popular revolt that ended in the ouster of Mubarak, who ruled for three decades. Although the jubilation of that event faded into a turbulent and divisive transition period, the square remains a powerful symbol, and on Saturday it pulsated with thousands of Brotherhood backers promising continued demonstrations if Morsi does not win.

On the other side of town, thousands of pro-Shafiq and pro-military demonstrators staged their largest gathering yet. “The people and the army — one hand,” some shouted.

Tensions are simmering after a tumultuous two weeks during which the military dissolved the Islamist-dominated parliament, instituted martial law and issued a decree that stripped powers from the future president. The moves were denounced by many activists and analysts as bids by the generals to cement their grip.

On Saturday, doubts abounded about the legitimacy of the official election results, and whether they would be announced at all Sunday. In recent days, an information vacuum has inflated with rumors about backroom dealings between the military chiefs, who are believed to support Shafiq, and the Brotherhood. Although the Brotherhood spoke defiantly this week about the apparent military power play, it has at times cooperated with the generals since the revolution.

The negotiations have been publicly confirmed by members of both groups and denied by others. Normally reliable sources of information, such as the state-owned al-Ahram English news service, have reported contradictory stories, adding to the intrigue.

This weekend, the service, citing anonymous government officials, reported that Shafiq would be named the winner on Sunday night. It later reported that the Brotherhood and the military council were negotiating, and that a deal would likely end in a Morsi victory.

Other news outlets went further. One, al-Dostour, said in a headline that the Brotherhood was planning a “massacre of the century” if Morsi loses. The Brotherhood’s political party said it would sue for libel and defamation.

Whatever the truth, many Egyptians believe that the winner, and the terms under which he will lead, are being brokered.

“The credibility of the incoming president has already been compromised,” said Khaled Fahmy, chairman of the history department at the American University in Cairo. “The result of the election is going to be tainted by this very confusing process."

A few blocks from Tahrir Square on Saturday afternoon, the rumor mill churned. Business owner Salma Saleh, 53, sipped tea and said she’d heard those demonstrating in the square were armed (they were not, at least not outwardly so). She said she thought a Shafiq win would ensure stability.

Nearby, a man buying carrots from Souad Metwali grumbled that election outcome was being rigged by Field Marshal Mohammed Hussein Tantawi, Egypt’s top general.

Metwali, 54, shrugged.

“We’ll just have to trust whatever is announced,” she said. “Because we haven’t seen anything with our own eyes.”

Correspondent Ernesto Londono and special correspondent Haitham Mohamed contributed to this report.