Several people were killed Friday in Cairo's Tahrir Square when supporters of ousted president Mohamed Morsi confronted their opponents shortly after a defiant speech by the leader of the Muslim Brotherhood.

The violence came as Egypt's Islamist movement is fractured by the military's ousting of the country's first-ever democratically elected president, a politician whose critics say broke promises and burned bridges with almost every segment of Egyptian society except his own Muslim Brotherhood, and was pushing the country toward an authoritarian religious state.

In his speech, about an hour before the violence, the Brotherhood's supreme guide, Mohammed Badie told his followers "we are sure of the promise of Allah" that Islamists will be victorious and "May the Lord destroy" the secular opponents of the Islamist movement.

"Our bare chests are stronger than bullets," Badie said.

Security forces opened fire and killed at least three Brotherhood supporters earlier in the day when demonstrators defied orders and approached a razor-wire barricade at the Republican Guard headquarters and attached a poster of Morsi to the barricade.

Later, Morsi's followers advanced on Tahrir Square, which has been occupied for days by Morsi's opponents who cheered his ouster by the military on Wednesday.

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Adham AbdelSalam, an Egyptian television and radio presenter, tweeted reports and photos from the square showing injured civilians and a rifle bullet casing in his hand.

"At #tahrir now... sounds of machine / automatic gun fire from pro #morsi supporters shot at protesters now," AbdelSalam wrote from @AdhamNileFm. "Live from #tahrir... one more dead... by pro #morsi bullets.."

A spokesman for the Muslim Brotherhood, Gehad El-Haddad, issued a message on his Twitter account calling for calm.

"We call on all Egyptian people to remain peaceful and call on law enforcement agencies to do their job at Maspero & in Alexandria," he wrote earlier in the day.

Later, El-Haddad tweeted that "Pro #Legitimacy protest being chased by attacking thugs while returning 2 Cairo University & no Military on site !! #SCAF #Failure…"

The Associated Press reported that two armored vehicles responded to the shooting in Tahrir Square. Helicopters flew overhead during the shootings, but did not intervene, according to AbdelSalam's reporting.

Analysts said the violence may get worse as the Brotherhood crowds grow, but that it might be tempered by the military's cautious approach and divisions among Egypt's Islamists.

Egypt's Salafis, the ultra-fundamentalist Islamists who want their literal interpretation of religious law enacted immediately, "are not on the same page" as the Brotherhood, which they now see as weakened, said Tawfik Hamid, a former Islamic radical from Egypt who's now a senior fellow at the Potomac Institute for Policy Studies in Washington. "They don't want to join a failing horse."

Nader Bakar, one of the leaders of the Salafi's Nour Party, Friday urged the Brotherhood to seek a peaceful resolution and subjugate itself to the will of Egypt's people, Hamid said.

The Salafis, who have less of a following in Egypt than the Brotherhood, "are worried that if they join the Brotherhood while they're a minority and the Brotherhood is out of power, the people will attack their homes and their (the Salafis') women and children," Hamid said.

Staying on the sidelines for now may allow the Islamist dream to survive, and give the Salafis "a chance to convince people that the problem is not Islam, it is the Muslim Brotherhood," Hamid said.

The Nour party did not oppose the roadmap described by the military when Morsi was deposed, and the Salafist leadership may be staying out of the fray, but its members have taken to the street with the Brotherhood, said Walid Phares, author of the "The Coming Revolution: Struggle for Freedom in the Middle East."

On the other hand, Egypt's Jihadis, fundamentalist Islamists who believe their goals can only be achieved through violence, have already begun to launch small attacks across the Egyptian mainland, and al-Qaeda-linked groups in the Sinai announced on Thursday a new emirate, or kingdom, in that sparsely populated desert expanse on the border with Israel.

The al-Qaeda-linked groups in the Sinai are not connected to the Brotherhood and other peaceful Islamic networks, and they announce "every day a new name," Phares said. "They want to create an emirate and create a no-go zone for the Egyptian army."

Phares believes the military is handling the unrest with deliberate restraint – allowing the Brotherhood to mobilize, march and give speeches accusing the military of being pro-American and pro-Israel – in order to provide a relief valve for Islamist anger and to send a message to the world that the army is giving them a voice, "to disarm the idea this is a coup," Phares said.

That approach can only last so long, however, before violence will flare, said Shadi Hamid, director of research at the Brookings Institution Doha Center.

Even if the Brotherhood calls for calm, it can't control all its supporters, Shadi Hamid said. And while the Brotherhood demonstrations so far were smaller than those of Morsi's opponents prior to his ouster, demonstrators still numbered in the hundreds of thousands.

And those demonstrations are likely to become bigger and more difficult to control, he said.

Brotherhood leaders "have been telling their supporters for the past week that (electoral) legitimacy is something worth fighting and dying for," Shadi Hamid said. "They feel betrayed and that they've been robbed of their rightful victory of the elected president. When you use that strong language, it's very difficult to come two days later and say never mind."

Egypt's now has "dueling legitimacies" between one camp that believe Morsi is the rightful president and the other camp supporting Adly Mansour, the man appointed to replace Morsi, Shadi Hamid said. "I think we're going to see more violence and the kind of clashes we see today."