Egypt's Hosni Mubarak was on life support after suffering a stroke in prison Tuesday, deepening the country's uncertainty just as a potentially explosive fight opened over who will succeed him.
Mubarak, 84, suffered a "fast deterioration of his health" and his heart stopped beating, the state news agency MENA and security officials said. He was revived by defibrillation but then had a stroke and was moved from Torah Prison to a military hospital in Cairo.
MENA initially reported he was "clinically dead" upon arrival, but a security official said he was put on life support.
Maj. Gen. Mohsen el-Fangari, a member of the ruling military council, told the Al-Shorouk newspaper website that Mubarak was in a "very critical condition," but denied he was dead. Mubarak's wife, Suzanne, came to the hospital, where Mubarak was in an intensive care unit, another security official said.
The developments came amid threats of new unrest and political power struggles, 16 months after Mubarak was ousted by a popular uprising demanding democracy.
Earlier Tuesday, both candidates in last weekend's presidential election claimed victory.
The Muslim Brotherhood, emboldened by its claim that its candidate won the election, sent tens of thousands of supporters into the street in an escalation of its confrontation against the ruling generals who invoked sweeping powers this week that give them dominance over the next president.
Some 50,000 protesters, mostly Islamists, protested in Cairo's Tahrir Square, chanting slogans in support of Brotherhood candidate Mohammed Morsi and denouncing the generals.
"It is not possible to have a revolution and then have military rule and a president with no authority," said protester Mohammed Abdel-Hameed, 48, a schoolmaster who came with his son from Fayyoum, an oasis province 60 miles southwest of Cairo.
The conflicting claims over the election could further stoke the heat. The campaign of Mubarak's former prime minister, Ahmed Shafiq, said Tuesday he won the election, denying the Brotherhood's claim of victory. Hundreds of Shafiq's supporters took to the streets in Cairo in celebration.
The election commission is to announce the official final results on Thursday, and either way the loser is likely to reject the result.
If Shafiq wins, it could spark an explosive backlash from the Brotherhood, which has said Shafiq could only win by fraud.
Mubarak has been serving a life sentence at Torah Prison for failing to stop the killing of protesters during the 18-day uprising against his rule last year.
The multiple disputes have turned a moment that was once anticipated by some as a landmark in Egypt's post-Mubarak transition -- the election of the first civilian president in 60 years -- into a potentially destabilizing snarl.
Just as polls closed Sunday night, the military -- which has ruled since Mubarak fell on Feb. 11, 2011 -- issued a constitutional declaration giving themselves power that all but subordinates the new president.
Tens of thousands demonstrated in Cairo and the Mediterranean port city of Alexandria on Tuesday evening to denounce the constitutional declaration.
The estimated 50,000 protesters in Cairo's Tahrir Square, birthplace of last year's anti-Mubarak uprising, were mostly Brotherhood supporters and other Islamists joined by a small group of leftist and liberal activists.