At least 74 people have been killed and 2,000 injured over five days of protests in Egypt, the country's security officials said Saturday, as violent clashes between demonstrators and police continued in the capital.

The officials, who spoke on condition of anonymity because they are not authorized to speak to the media, said the casualties include both protesters and security forces who have been injured or killed.

The news came hours after Egyptian police opened fire on a massive crowd attempting to storm the offices of the Interior Ministry in downtown Cairo, killing at least three demonstrators as the protests demanding the ouster of President Hosni Mubarak took another deadly turn.

The bodies of the dead protesters were carried on the shoulders of a chanting crowd.

The clash came shortly after a government-imposed curfew went into effect at 4 p.m. local time, following a relatively peaceful day of protest.

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

Some observers speculated that security personnel loyal to Mubarak could be behind some of the looting.

"My perception is these thugs on the street are in large part members of the security services," said Michael Bell, Canada's former ambassador to Egypt.

"If one is cynical enough, one could suppose that these guys are sent into the street to create fear about individual security" to draw people away from the protests and to make them more sympathetic to the president's autocratic style of rule, Bell told CTV News Channel.

Egyptian soldiers in tanks and armoured personnel carriers fanned out across the city to protect government buildings, as well as the Egyptian Museum, which houses many of Egypt's most treasured antiquities. Troops also blocked access to the pyramids outside Cairo.

After attacking police vehicles and buildings in Cairo, as well as Alexandria and Suez, on Friday, protesters overran a police station in the Cairo neighbourhood of Giza Saturday before setting fire to the building.

Protesters remained in Cairo's Tahrir Square Saturday evening, even as Mubarak's Cabinet resigned on the orders of the president.

State television reported that Mubarak also named a new vice-president on Saturday, choosing his intelligence chief and close confidant Omar Suleiman to the post.

It was not immediately clear how the announcement would impact public demands that Mubarak leave his post after 30 years of authoritarian rule. But protester Mohammed Mahmoud appeared to echo the sentiments of many when he said: "What we want is for Mubarak to leave, not just his government. We will not stop protesting until he goes."

Mubarak has refused to meet the protesters' demands to step but pledged to usher in political reform.

The concession did little to stem the tide, as protesters have been prompted by anger over the country's crushing poverty, unemployment and corruption.

For five days, crowds have overwhelmed police forces in Cairo and other major cities, often accompanied by rock attacks and firebombs.

Armoured vehicles and military forces were posted overnight near government buildings and around demonstration sites such as Tahrir Square. Unlike police forces, which are loathed for their cruelty, protesters appeared to accept the military presence.

Saad Abedine, a CNN reporter posted in Cairo, told CTV News Channel protesters did not appear swayed by Mubarak's promised changes, saying the president has lost the respect of the people.

"Everybody is shouting for one thing. It is a time for the whole system to just collapse and bring in new people, a new regime," he said. "They don't believe that the government is enough. They want the parliament to be gone, they want free elections and they want the president definitely to resign."

During the worst of the clash on Friday, protesters attacked the ruling party's headquarters, burning the facility to the ground.

In a televised address, Mubarak dismissed his Cabinet and made vague promises of social reform while accusing protesters of plotting to destabilize Egypt by destroying the legitimacy of his regime.

The address outraged protesters who stayed in the streets well into the night, chanting for an end to his three-decade of authoritarian rule.

Cell phone and Internet service was cut off earlier in the conflict, but reports suggested that cell phones were working Saturday morning. Internet service appeared to remain blocked, hampering protesters who used social networking sites to organize.

The situation prompted criticism from U.S. President Barack Obama, who asked Mubarek to take concrete steps to improve human rights.

Obama's government threatened to reduce its $1.5 billion foreign aid program if the Egyptian government, Washington's most important Arab ally, escalated the use of force.

Foreign affairs experts derided Mubarak's decision to dismiss his government's cabinet as shortsighted, saying that a change to his staff would not satisfy those calling for constitutional change.

Speaking from the World Economic Forum in Davos, Switzerland, U.S. Senator John Kerry called for Mubarak to respond to his citizen, adding that the dismissal of his government didn't address those issues.

"I think that we have to see how things move today and, obviously, the key here is for President Mubarak to respond to the needs of his people in a way that is more directly connected to their frustrations, much more so than apparently yesterday's speech succeeded in doing," Kerry told The Associated Press.

With files from The Associated Press