Egypt is bracing for more unrest after election officials postponed the announcement of a winner in the nation's first freely-contested presidential elections.

The election commission cited hundreds of complaints lodged by both presidential candidates — the Muslim Brotherhood's Mohammed Morsi and his rival, former prime minister Ahmed Shafiq — for the indefinite postponement.

Both sides are claiming victory, and supporters of both men threatened a backlash should their candidate lose.

Aides to the Islamist Brotherhood's candidate said Mr. Morsi received 52 percent to Mr. Shafiq's 48 percent. The Shafiq camp countered that the former air force commander won with 51.5 percent of the vote.

Morsi supporters, worried that the delay could be an attempt to alter the unofficial results which appeared to give their candidate the lead, gathered in Cairo's Tahrir Square late Thursday, demanding a quick resolution to the country's political crisis.

But the Shafiq campaign said late Wednesday that its candidate would accept the results.

The postponement of election results is only part of the political standoff. In the past week, the ruling Supreme Council of the Armed Forces carried out a series of power grabs, including the court-ordered dissolution of the Islamist-dominated parliament.

The council also declared an interim constitution that gives its generals and the courts final say over much domestic and foreign policy, as well as the process to create a new permanent constitution.

Another element adding to the sense of uncertainty is the health of 84-year-old former president Hosni Mubarak, who was ousted in Egypt's uprising last year and is now serving a life prison sentence for failing to stop the killing of protesters during the revolt.

In Washington, U.S. Secretary of State Hillary Clinton said Egypt's military must “fulfill its promise” to turn over power to the winner of a presidential runoff vote. In a TV interview broadcast late Wednesday, Clinton called the military's actions “clearly troubling.”

Clinton said Egypt needs an “inclusive democratic process” that respects the rights of all Egyptians.

“The military has to assume an appropriate role, which is not to try to interfere with, dominate or subvert the constitutional authority. They have to get a constitution written. There's a lot of work ahead of them.”