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Heavy gunfire rang out in Cairo's central square early Thursday morning and a protest organizer said at least three anti-government demonstrators were killed.

Mustafa al-Naggar said he saw three bodies being taken to an ambulance and that automatic weapons fire directed at the square came from at least three directions.

Supporters of Egyptian President Hosni Mubarak flooded into Tahrir Square on Wednesday, some riding camels or on horseback, attacking protesters who want an immediate change of government in the Arab world's most populous country.

Egyptian Health Minister Ahmed Sameh Farid said three people died and at least 611 people were injured in the fighting, which coincided with the first mass display of support for the country's embattled president since widespread protests broke out Jan. 25.

One man who died after falling from a bridge is believed to have been a member of the country's security forces, Farid said. He was dressed in civilian clothes at the time of his death. He said authorities are investigating the incident.

Anti-government protesters who have flooded the streets of Egypt's cities in recent days blame 82-year-old Mubarak for an array of economic and social problems that have afflicted his people during his 30 reign.

Some of Mubarak's supporters brandished whips as they charged into Tahrir Square, or Freedom Square, which has become the heart of the demonstrations in downtown Cairo. Others threw firebombs from rooftops in what many observers described as an organized offensive against protesters seeking to topple the Egyptian leader.

Anti-government protesters accused Mubarak and his allies of dispatching paid thugs and plainclothes police to bring the uprising to a quick and bloody end. Some brandished identification badges they said were stolen from their attackers. Government workers also reported being ordered into the streets by their employer.

"After our revolution, they want to send people here to ruin it for us," said Ahmed Abdullah, a lawyer protesting against Mubarak in Tahrir Square. "Why do they want us to be at each other's throats, with the whole world watching us?"

Many of the president's supporters carried flags that appeared as though they had been freshly handed out, CTV's Martin Seemungal reported from a balcony overlooking Tahrir Square.

The push of pro-government forces also coincided with a number of assaults on foreign journalists, including anchors from major American news outlets and at least one Canadian cameraman.

Protests persist

Wednesdays clashes stood in stark contrast mass demonstrations held a day earlier, in which several million anti-Mubarak protesters from all walks of life took to the streets in a largely peaceful show of force.

The country's president has said that he will not run in the country's next elections, which are scheduled for September. However, protesters want the autocratic leader to step down immediately, paving the way for a new government.

Throughout Tahrir Square, which has become the symbolic heart of the demonstrations in downtown Cairo, Mubarak supporters and their opponents threw bottles and chunks of concrete at one another, or engaged in fistfights that left them bruised and bloodied.

Makeshift health clinics were set up by the anti-government protesters in nearby mosques and alleyways to treat the wounded.

State television broadcast an order for all protesters to leave the square late Wednesday. But the confrontation between the pro- and anti-government factions continued for hours afterward.

Sporadic gunfire could be heard as the two sides dug in their heels under a setting sun. They lobbed Molotov cocktails at each other and shielded themselves behind sheets of corrugated metal.

It wasn't clear whether the military was firing into the air in an effort to disperse the crowd, or whether the shots originated with either of the protest groups and had a more lethal intent.

At one point, CTV's Lisa LaFlamme reported from the edge of Tahrir Square that tanks had moved into the area and were driving toward the protesters, sending many of them running for cover. But the military's role remained largely passive.

Clashes that raged throughout the day left fires burning in the square, as well as in front of the famed Egyptian Museum. Efforts were underway to control the flames, LaFlamme said.

Chaotic situation

Ali Mikkawi, an Egyptian-Canadian who has been helping to organize protests in Cairo, said it was difficult to say who was behind the clashes on the pro-Mubarak side.

"It's just chaos," Mikkawi told Â鶹ӰÊÓ Channel in a telephone interview from Cairo, adding that anti-government protesters had discovered at least one pro-Mubarak supporter carrying police identification.

So far, the Egyptian army has opted not to intervene in the clashes, underscoring the mostly "neutral stance" the army has taken since the anti-Mubarak protests began, Seemungal said.

Earlier Wednesday, the army asked the anti-government protesters to end their demonstrations against Mubarak, arguing that the protesters' message has been heard and that it is time to resume daily routines in Cairo.

Military spokesperson Ismail Etman went on television to address the protesters, who have held demonstrations in Cairo's Tahrir Square for the past nine days.

Etman asked the protesters to stand down "out of love for Egypt," so that the country can chart a path back to stability.

"You have started coming out to express your demands and you are the ones capable of returning normal life to Egypt," Etman said.

"Your message has arrived, your demands have become known."

International reaction

The escalating violence also led to swift condemnation from the international community.

On Wednesday, White House spokesperson Robert Gibbs said the U.S. "deplores and condemns the violence that is taking place in Egypt."

In Britain, Prime Minister David Cameron said Egyptian authorities must move quickly to bring in political reforms, and said "if it turns out that the regime in any way has been sponsoring or tolerating this violence, that would be completely and utterly unacceptable." UN Secretary-General Ban Ki-moon, who was meeting Cameron in London Wednesday, also called the violence "unacceptable."

The 82-year-old Mubarak announced he will not run for office in upcoming elections this fall -- yet opposition groups involved in the demonstrations have indicated they want him to leave office as soon as possible.

With files from The Associated Press