Egyptian troops have opened fire on supporters of ousted president Mohammed Morsi as they marched on a Republican Guard facility.
Witnesses said Republican Guard forces opened fire when protesters approached a barbed wire barrier around the facility and hung a picture of Mr Morsi on it.
Several protesters fell wounded, including at least one severely with a bloody wound to the head.
It came as tens of thousands of people protested across Egypt over the ousting of Mr Morsi by the military.
The demonstrators, mainly Islamists, vowed to restore him to office.
A crowd of Morsi supporters had filled much of a broad boulevard outside a Cairo mosque, vowing to remain in place until the Islamist leader, who was Egypt’s first freely elected president, is returned to office.
The protesters railed against what they called the return of the regime of autocrat Hosni Mubarak, ousted in early 2011.
The crowd then began to march on the headquarters of the Republican Guard, many chanting: “After sunset, president Morsi will be back in the palace.”
The military forced Mr Morsi out on Wednesday after millions of Egyptians turned out in four days of protests demanding his removal, saying he had squandered his electoral mandate by putting power in the hands of his own Muslim Brotherhood and other, harder-line Islamists.
In the 48 hours since, the military has moved against the Brotherhood’s senior leadership, putting Mr Morsi under detention and arresting the group’s supreme leader and a string of other figures.
“The old regime has come back ... worse than before,” said Ismail Abdel-Mohsen, an 18-year old student among the crowds outside the Rabia al-Adawiya Mosque.
He dismissed the new interim head of state sworn in a day earlier, senior judge Adly Mansour, as “the military puppet”.
The crowd began to march on the headquarters of the Republican Guard, many chanting: “After sunset, president Morsi will be back in the palace.”
Meanwhile, the African Union has suspended Egypt from membership in the continental body.
AU Commission head Nkosazana Dlamini-Zuma told a news conference in the Ethiopian capital, Addis Ababa, that the removal of Mr Morsi falls under the AU doctrine on unconstitutional changes of government.
AU officials decided Friday to block Egypt from all activities of the continental body until constitutional order is restored in the nation, she said.
The Muslim Brotherhood called for Friday’s protests, which took place at several sites around the capital and in other cities. Brotherhood officials underlined strongly to their followers that their rallies should be peaceful.
But there are serious fears that more extremist groups who gain considerable influence during Mr Morsi’s year in office will lash out with a campaign of violence.
In the early hours of Friday, masked assailants launched a coordinated attack with rockets, rocket-propelled grenades and anti-aircraft guns on the airport in el-Arish, the provincial capital of northern Sinai, as well as a security forces camp in Rafah on the border with Gaza and five other military and police posts. At least one soldier was killed in nearly four hours of clashes that ensued.
Islamic militants hold a powerful sway in the lawless and chaotic northern Sinai. They are heavily armed with weapons smuggled from Libya and have links with militants in the neighbouring Gaza Strip, run by Hamas.
After the attack, Egypt indefinitely closed its border crossing into Gaza, sending 200 Palestinians back into the territory, said General Sami Metwali, director of Rafah passage.
Mr Morsi supporters say the military has wrecked Egypt’s democracy by carrying out a coup against an elected leader. They accuse Mubarak loyalists and liberal and secular opposition parties of turning to the army for help because they lost at the polls to Islamists. But many supporters have equally seen it as a conspiracy against Islam.
Many at today’s protests held copies of the Quran in the air, and much of the crowd had the long beards of ultraconservative men or encompassing black robes and veils worn by women, leaving only the eyes visible.
One protester shouted that the sheik of Al-Azhar – Egypt’s top Muslim cleric who backed the military’s move – was “an agent of the Christians”, reflecting a sentiment that the Christian minority was behind Mr Morsi’s removal.
The protesters set up “self-defense” teams, with men staffing checkpoints touting sticks and home-made body shields. There was no significant presence of military forces near the protests.
The night before, the military spokesman issued a statement urging all protesters to remain peaceful. In a message to Morsi’s opponents, Colonel Ahmed Mohammed Ali warned against “gloating,” vengeance or attacks on Brotherhood offices, saying there must not be an “endless cycle of revenge”.
The military has a “strong will to ensure national reconciliation, constructive justice and tolerance,” he wrote in an official Facebook posting. He added that the army and security forces will not take “any exceptional or arbitrary measures” against any political group.
But the Brotherhood has been furious over the arrests of its top leaders, as well as the closure of its TV station Misr25, its newspaper, and three other Islamist television stations. It called to move a return to Egypt’s “dark, repressive, dictatorial and corrupt ages”.
Mr Morsi has been under detention in an unknown location since Wednesday night, and at least a dozen of his top aides and advisers have been under what is described as “house arrest,” though their locations are also unknown.
Besides the Brotherhood’s top leader, General Guide Mohammed Badie, security officials have also arrested his predecessor, Mahdi Akef, and one of his two deputies, Rashad Bayoumi, as well as Saad el-Katatni, head of the Brotherhood’s Freedom and Justice Party, and ultraconservative Salafi figure Hazem Abu Ismail, who has a considerable street following.
The National Salvation Front, the top opposition political group during Mr Morsi’s presidency and a key member of the coalition that worked with the military in his removal, criticised the moves, saying: “We totally reject excluding any party, particularly political Islamic groups.”