Egyptian security sources say ousted President Hosni Mubarak is unconscious and on a respirator after he was rushed from prison to a military hospital following a stroke.

Earlier reports by the state news agency MENA said Mubarak's doctors had declared the former leader “clinically dead” when he arrived at Maadi Hospital in southern Cairo after being transferred from nearby Torah Prison. It said doctors were unable to revive Mubarak after he went into cardiac arrest.

Military officials acknowledged early Wednesday that Mubarak had suffered a stroke, but said he is currently “using artificial respiration” and that “it is still early to say he is clinically dead.”

The ousted leader had ruled Egypt for 30 years until he was overthrown last February by a revolution during the “Arab Spring'' protests that roiled the region. The 84-year-old had been sentenced to life in prison earlier this month for failing to stop the killing of protesters during the popular uprising.

The confusion over Mubarak's state of health came as tens of thousands of Egyptians from across the political spectrum packed central Cairo to protest a declaration by Egypt's ruling generals extending their grip on power.

As protest numbers swelled Tuesday, Egypt's election commission said it was evaluating hundreds of complaints of irregularities in the runoff presidential election between the Muslim Brotherhood's Mohammed Morsi and former prime minister Ahmed Shafiq.

Both candidates claimed victory, but a public count of the ballots, confirmed by the official media, showed Mr. Morsi winning with 52 percent of the vote to Mr. Shafiq's 48 percent. Aides of the establishment-backed Shafiq disputed the claim.

Turnout was just over 50 percent of the roughly 50 million eligible voters. Election officials are expected to announce the official results on Thursday, but the losing candidate is likely to reject the outcome as fraudulent.

International campaign observers, including the U.S.-based Carter Center, said Tuesday they were denied sufficient access and accused the military leadership of hampering the transition to democracy.

The Carter Center said it had been unable to monitor the vote properly and that a “return of elements of martial law” meant it was “now unclear whether a truly democratic transition remains under way in Egypt.”

The poll was Egypt's first freely contested presidential election.

The powerful Brotherhood movement has vowed to challenge the military's recent moves restoring martial law, dismissing the Islamist-dominated parliament and curbing the powers of the incoming president.

A unilaterally declared interim constitution grants the generals and the courts final say over much domestic and foreign policy and the constitutional drafting process. It rules that no election can be held until a military-appointed panel writes a permanent constitution whose articles the generals can veto.

Despite the moves, the ruling Supreme Council of the Armed Forces vowed earlier this week to honor its promise to hand over power to Egypt's newly elected president by the end of the month.

The U.S. State Department has said the Obama administration will hold the SCAF to its promises for an “inclusive constitutional drafting process, the timely seating of a democratically elected parliament, and the swift, permanent transfer of power to a civilian government.”

The U.S. has provided billions in military aid to Egypt over three decades of close relations.