Mohamed ElBaradei, a Nobel Peace laureate and Egypt's most influential democracy advocate, called on President Hosni Mubarak to step down as thousands of protesters in the capital defied a government-ordered curfew for a third night.

ElBaradei, who is also the former head of the UN's atomic energy agency, gave a brief speech at a demonstration in Cairo's Tahrir Square, or Liberation Square, joining a chorus of voices calling for an end to poverty, unemployment, widespread corruption and police brutality in the Arab world's most populous country.

"You are the owners of this revolution. You are the future," ElBaradei told the cheering crowd. "Our essential demand is the departure of the regime and the beginning of a new Egypt in which each Egyptian lives in virtue, freedom and dignity."

Meanwhile Egypt's powerful military stepped up its presence in Cairo on Sunday, closing roads with tanks and sending F-16 fighter jets streaking across the skyline while leaving the crowd of thousands gathered at Tahrir Square -- the centre of the demonstrations -- untouched.

Low-flying fighter jets blasted over the protests through the day, in an apparent attempt to underline the military's control of a city overrun by looting, armed robbery and anti-government demonstrations.

Police also returned to city streets on Sunday after virtually disappearing for days and creating a security vacuum only partially filled by the military presence.

Army's role

Unlike police forces, which are loathed for their cruelty, protesters appeared to accept the military presence.

Up to 10,000 chanting protesters remained at the heart of Egypt's capital city well after a government-issued curfew had passed, shouting for an end to the 30-year rule of Egyptian President Hosni Mubarak.

A spokesperson for the outlawed Muslim Brotherhood, which is seeking an Islamist state in Egypt, told The Associated Press that members of the group had also joined the demonstration, now well into its sixth day.

With growing signs of the military's authority on the street, some protesters at Tahir Square hoisted banners that seemed to capture the country's uncertain political situation.

"The army must chose between Egypt and Mubarak," the banners read.

The army had sent hundreds of troops and armoured vehicles into the streets of Cairo and other cities after a night of violence across the country.

After police initially clashed with protesters, they disappeared mysteriously on Friday, paving the way for looting, arson and robberies in various Egyptian cities.

Hundreds of Muslim militants were freed from jails and thousand of other inmates vanished as protests in Egypt descended into anarchy through the day.

Gangs of armed men attacked at least four jails across Egypt before dawn, while shopping malls and the streets of Cairo were similarly overrun.

Egyptian security officials said they were hunting the escaped prisoners. Those who escaped include 34 members of the outlawed Muslim Brotherhood.

Pressure from Washington

Many protesters accused the police of intentionally allowing looting to spread fear and chaos in an effort to weaken the demonstrations.

President Mubarak has long been considered one of America's closest allies in the region, with Washington sending his government more than US$1.5 billion in aid each year.

But in a growing sign of Mubarak's weakening position, Secretary of State Hillary Rodham Clinton spoke of the need for an "orderly transition to democracy" in the country of 80 million people.

"We have been very clear that we want to see a transition to democracy, and we want to see the kind of steps taken that will bring that about," Clinton told Fox News on Sunday.

The U.S. Embassy in Cairo told Americans to consider leaving the country as soon as possible and has authorized the voluntary departure of families and non-emergency employees.

Canada has also cautioned citizens against non-essential travel to Egypt and to avoid large cities, where citizens are now in their sixth day of protesting Mubarak's rule.

Mubarak has so far ignored calls to leave office, promising only to usher in political reform. On Saturday, he named his intelligence chief Omar Suleiman to the new role of vice president.

Suleiman's new position establishes him as a likely successor should Mubarak leave office. Ahmed Shafiq, the outgoing civil aviation minister and Mubarak's fellow former air force officer, was named prime minister.

Questions over death toll

At least 97 people have been killed and thousands have been injured in violent clashes over the past six days, according to the official count. However, reports from witnesses across Egypt suggest the actual death toll could be significantly higher.

Analyst Kamran Bokhari of the private intelligence firm Stratfor said increasing looting and violence might force the military into action.

"The question is whether the military is going to align with President Mubarak and force protesters off of the streets," Bokhari told CTV News Channel on Sunday. "So far there is no evidence that that is happening. There seems to be some consideration going on by the military leadership."

Earlier on Sunday, the military worked with civilian volunteers to check IDs and bags of people arriving for demonstrations at Tahrir Square. Soldiers and volunteers said they were checking for weapons, but also searching for plainclothes police who may be trying to enter the square.

A man concealing a kitchen knife was stopped in one instance and reportedly beaten and detained in a military vehicle.

As public demonstrations carried on, so did looting, spurring residents of Cairo's more affluent neighbourhoods to board up their homes.

On Sunday, state television showed Mubarak during what was said to be a visit to the country's military command centre. The president looked sombre and fatigued during his first public appearance since a television appearance on Friday.

An unprecedented Internet cutoff remained in effect in an apparent move to disrupt the organization of demonstrators. Meantime, state television reported that the government had closed the Cairo office of the Qatar-based Al-Jazeera television network.

With files from The Associated Press