Egypt's Islamist and liberal forces, wary about the results of the weekend's presidential election, cast aside their ideological differences to protest the ruling military's moves to extend its grip on power.

As protest numbers swelled into the tens of thousands Cairo's Tahrir Square on Tuesday, the elections commission said it was evaluating hundreds of complaints in the runoff contest between the Muslim Brotherhood's Mohammed Morsi and former Prime Minister Ahmed Shafiq, both of whom each claimed victory. Official results are expected to be announced on Thursday.

The united effort in Tahrir Square offered the first indication that liberal-minded political groups are willing to rally behind the powerful Muslim Brotherhood to check the military leadership's widening hold on Egypt's emerging political system.

The turnout on Tuesday marked a step toward repudiating what some analysts say is the military leadership's divide-and-conquer strategy. Egypt's liberal-minded activists, who form the core of the protest movement, and the Islamists, who have won huge successes at the ballot box have spent much of the past year at odds.

'No Salafi, no liberal, no Brotherhood, today it's only Egyptian,' sang one large group of protesters in Tahrir Square, the focal point of the uprising that ousted President Hosni Mubarak last year and left the military in charge of a political transition.

On Tuesday, doctors were considering transfering the deposed president to a military hospital from a prison outside Cairo, where the 84-year-old suffered a stroke, according to official state news media reports. Mr. Mubarak was sentenced to life in prison this month on charges of complicity to murder.

A shift in mood was palpable in Tahrir Square on Tuesday. When Egypt's Supreme Constitutional Court dissolved parliament two weeks ago, the outrage was barely felt. Many activists accused the military of orchestrating a soft coup, but the few calls for mass protest were largely ignored.

Some liberal-minded politicians, including those who have been critical of military rule, publicly praised the court's decision to dissolve the Islamist-dominated assembly that many of them saw as a prelude to an Islamist putsch.

But on Tuesday evening, protesters projected a unified message.

On a hastily built stage on the western edge of Tahrir Square, speakers from the secular-minded April 6th Youth Movement and the Muslim Brotherhood took turns addressing the crowd.

Meanwhile, Egypt's political future hung in the balance as rival campaigns claimed victory and reports of fraud and irregularities piled up.

The Muslim Brotherhood, holding a news conference on Tuesday morning repeated its report that Mr. Morsi had won 52% of the vote to Mr. Shafiq's 48%.

In another news conference across town, campaigners for Mr. Shafiq retorted that their candidate was in the lead with 51.5%.

In a sign of legal battles to come, a Shafiq campaign manager said Mr. Shafiq and his supporters are 'prepared to go to the furthest point possible to prove that Shafiq is Egypt's next president.'

International campaign observers, including the Atlanta-based Carter Center, complained that the Egyptian government offered limited access to their observers. But monitors noted only a few isolated cases of administrative errors, and none of the organizations declared the vote invalid.

Matt Bradley / Charles Levinson / Tamer El-Ghobashy