CAIRO — Egypt's deposed president Hosni Mubarak was placed on life support after suffering a stroke in prison on Tuesday, deepening the country's uncertainty just as a potentially explosive fight opened over who will succeed him.

The 84-year-old Mubarak suffered a "fast deterioration of his health" and his heart stopped beating, the news agency MENA and security officials said. He was revived by defibrillation but then had a stroke and was moved from Tora Prison to a military hospital in Cairo.

MENA initially reported he was "clinically dead" upon arrival, but a security official said Mubarak was put on life support. The official spoke on condition of anonymity because he was not authorized to speak to the media.

Maj. Gen. Mohsen el-Fangari, a member of the ruling military council, told the Al-Shorouk newspaper website that Mubarak was in "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. Mubarak's sons, Alaa and Gamal, were not allowed to accompany their father and were returned to prison, where they are currently being held on charges of stock market related corruption.

The developments came amid threats of new unrest and political power struggles, 16 months after Mubarak was ousted by a popular uprising demanding democracy. On Tuesday, both candidates in last weekend's presidential election declared victory. Following their own claim to victory, the Muslim Brotherhood 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.

"It is not possible to have a revolution and then have military rule and a president with no authority," said protester Mohammed Abdel-Hameed, a 48-year-old schoolmaster who came with his son from Fayyoum, an oasis province 60 miles (100 kilometers) southwest of Cairo.

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. Critics called it a coup intended to maintain their control over the state even after they nominally transfer authorities to the president by July. The declaration gave the generals legislative powers and control over the process of drafting a new constitution and the national budget. It also shields the military against any kind of civilian oversight and allows the generals to run their own affairs without interference from civilian authorities.

The election commission is to announce the official final results on Thursday. The campaign of Mubarak's former prime minister, Ahmed Shafiq, said on Tuesday he won the election, denying the Brotherhood's claim to victory. Shafiq is seen by his opponents as likely to preserve the military-backed police state that his former boss headed for three decades. If he were to win, it could spark an explosive backlash from the Brotherhood, which has said Shafiq could only win by fraud. Shafiq's campaign has focused on presenting him as a strongman able to keep Egypt stable and out of the hands of the Brotherhood, playing on fears the group will turn the country into an Islamic state.

The sudden health crisis of Mubarak, who is serving a life prison sentence, briefly overshadowed the political standoff. Moving Mubarak out of prison to Maadi military hospital is likely to further infuriate many in the public. Many Egyptians have been skeptical of earlier reports that his health was worsening since he was put in prison on June 2, believing the reports were just a pretext to move him to another facility. There is a widespread suspicion that security and military officials sympathetic to their old boss are giving him preferential treatment. Maadi is the same hospital where Mubarak's predecessor, Anwar Sadat, was declared dead more than 30 years ago after being gunned down by Islamic militants.

Mubarak's condition brought to mind former Israeli Prime Minister Ariel Sharon — though it was not known if there was any medical similarity in their conditions. Sharon, now 84, suffered a massive stroke in 2006. Intensive treatment and repeated operations by a team of brain surgeons stabilized his condition, but he has never regained consciousness and remains on life support in a deep coma.

Mubarak has been serving a life sentence at Tora Prison for failing to stop the killing of protesters during the 18-day uprising against his rule last year. The verdict against him has already been a spark for protests — thousands massed in Tahrir when the court acquitted him and his sons on separate corruption charges and cleared several top security chiefs on the protester killings.