About 15 people were injured during clashes between Egypt's military and supporters of Mohammed Morsi Friday outside the barracks where the ousted Islamist president is believed to be detained.
The wounded people were being treated by medical staff at the scene for what appeared to be injuries from shotgun blasts. NBC News journalists saw people with injuries to their face and torso.
The violence broke out after about 6,000 people who had been protesting outside Cairo's Rabia al Adawiya Mosque marched toward the Republican Guard headquarters, where Morsi is rumored to have been held since being deposed by the military.
BBC News correspondent Jeremy Bowen said on Twitter that he could see a "bloodied dead body." NBC News could not confirm any fatalities.
Bowen later said he had been hit by shotgun fire.
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Television footage from the scene showed several bloodied people near the scene and clouds of tear gas. Large numbers of people were continuing to protest as soldiers stood behind barbed-wire barricades.
Two state-run television channels, Nile TV and ETV 1, both denied there had been any casualties, citing security sources.
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A statement on the Muslim Brotherhood's website said earlier that peaceful protest was "a right guaranteed to all Egyptians," saying it would hold the government responsible for its supporters' security.
The Islamists' protests were given various names, including the "Friday of Rage" and the "Friday of Rejection."
A liberal coalition also called for its supporters to take to the streets, saying that the Islamists' demonstrations could be a "counter-revolution," Reuters reported.
The Egyptian Army was put on a heightened state of alert in the Sinai region that borders Israel Friday. The border crossing between the Gaza Strip and Egypt at Rafah was also closed.
Sinai is a hotbed of Islamist militant activity and there has been concern in Israel about the potential for increased cross-border attacks if the Egyptian military becomes pre-occupied with dealing with the demonstrations.
At a rally in Northern Sinai after the ouster of Morsi, hundreds of people cheered as a local leader spoke of declaring a "war council" to fight the Egyptian military, the police and the state. However, a spokesman for a loose coalition of tribes rejected that saying they were with the military and would not support any violence against the state.
There were reports that a state of emergency had been imposed in the Sinai area, but this was later denied by the military.
Dozens of people have been killed in clashes between rival factions, police and soldiers since last weekend, with millions of people taking part in anti-Morsi protests.
Morsi was ousted as president by the military on Wednesday and replaced by top judge Adly Mansour on Thursday. Fresh elections have been promised.
The statement on the Brotherhood's website appealed to "the masses of the Egyptian people to mobilize in peaceful mass marches in all liberty squares and streets of Egypt, to be started from all mosques, after Friday prayers, to reject the heinous coup against popular will."
It was attributed to the "National Alliance in Support of Electoral Legitimacy."
"NASEL said that it feels rising public anger and the imminent danger threatening the nation as a result of the unprecedented military coup d'état against legitimacy derived from the will of the people," it said.
Morsi is under house arrest and the statement said NASEL would hold the "coup masterminds" responsible for his safety and "for preventing the elected president from contact with the people."
The Brotherhood denounced the crackdown, including the shutdown Wednesday night of its television channel, Misr25, its newspaper and three pro-Morsi Islamist TV stations. The military, it said, is returning Egypt to the practices of "the dark, repressive, dictatorial and corrupt ages."
On Thursday, a judge said that an investigation was being held into accusations that Morsi and eight other senior Muslim Brotherhood figures had defamed the judiciary. The arrests of Mohammed Badie, the Muslim Brotherhood's supreme guide, and a top deputy, Khairat el-Shater, were also ordered.
Authorities have issued a wanted list for more than 200 Brotherhood members and leaders of other Islamist groups.
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Military spokesman Col. Ahmed Mohammed Ali said in a Facebook posting that that the army and security forces will not take "any exceptional or arbitrary measures" against any political group, The Associated Press reported.
The military has a "strong will to ensure national reconciliation, constructive justice and tolerance," he wrote.
The National Salvation Front, the top opposition political group during Morsi's presidency, called for all sides – "particularly political Islamic groups" -- to be included in the new political process, the AP reported.
"Reconciliation is the name of the game, including the Muslim Brotherhood. We need to be inclusive," Munir Fakhry Abdel-Nour, a leading member of the group, told the news service. "The detentions are a mistake."
But the National Salvation Front, a liberal coalition, also issued an "urgent call" for supporters to take to the streets on Friday in response to Islamists' demonstrations.
NSF spokesman Khaled Dawoud told Reuters that plans by the Brotherhood and its allies to hold protests amounted to a "counter-revolution."
Egypt's newly appointed Foreign Minister Mohamed Kamel Amr said that Secretary of State John Kerry had expressed concern during a telephone call on Thursday for human rights, Reuters reported.
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"He was worried about the status of human rights," Amr said, adding this was understandable. "I assured him there is no retribution, no acts of vengeance, that nobody will be treated outside the law."
Amr, a career diplomat who tended his resignation to Mursi after Sunday's anti-government protests, said he had spent the day calling international counterparts and briefing ambassadors with the message that there had been no "military coup" in Egypt. The army had merely heeded the popular will.
Of his conversation with Kerry, he said: "I told him that the main aim of the military now is to maintain security."
"There will be no acts of violence, no acts of exclusion. Everybody will be included. The idea is to have everybody participating in the transitional process."
Reuters and The Associated Press contributed to this report.