At least three supporters of deposed President Morsi killed, as crowd marches on barracks where ousted leader is held.
At least three supporters of deposed Egyptian President Mohamed Morsi were killed by gunfire as a crowd of several hundred tried to march towards the military barracks in Cairo where he is believed to be held.
Al Jazeera's correspondent, reporting from near the military barracks, said several dozen people were also injured by shotgun pellets fired by the army.
"One protester broke away from the rally to stick a pro-Morsi poster on the barbed-wire around the barracks. He was shot in the head with birdshot," he said.
Security forces were cordoning the Republican Guard barracks but it was not immediately clear who had opened fire.
An army spokesman denied that troops opened fire on supporters, saying that soldiers were using only blank rounds and teargas. It was unclear whether security forces other than the army were present.
The interior ministry also denied that people were killed in the clashes outside the Republican Guards club.
In Nasr City in the Egyptian capital, thousands of supporters of Morsi gathered to protest against his ouster as the country's president in a military coup.
Senior Muslim Brotherhood member Mohamed ElBeltagy told the protestors: "Your brothers are now at the Republican Guards trying to help president Morsi get out. Your brothers are being fired at with live bullets.
"I call on the military is to remove the defence minister and to bring president Morsi back to power. We are going to the republican guards as martyrs in million. Today, president Morsi should come back to power," ElBeltagy said.
The crowds are expected to swell further after Friday afternoon prayers in response to the call by a coalition of Islamist groups led by the Muslim Brotherhood for demonstrations against the coup.
The coalition on Thursday urged people to take part in a "Friday of Rejection" protest following weekly prayers. The call is being seen as a test of whether Morsi still has a support base in the country, and how the army will deal with it.
Morsi, who was Egypt's first democratically elected president, belongs to the Muslim Brotherhood movement .
While the military coup came in the wake of mass protests seeking Morsi's dismissal, the ex-president's supporters are angry and have denounced the army's intervention.
They have vowed to continue with their sit-in protest and march towards the defence ministry.
Dozens of people were wounded in clashes in Morsi's home city Zagazig on Thursday, raising fears of more violence.
Al Jazeera's Jamal Elshayyal, reporting from Nasr City in Cairo, said:"People here say this is no longer only a pro-Morsi rally, it is about resisting the military coup as much as it is about reinstating te first and only ever democratically elected civilian president."
Earlier, the military had appealed for conciliation and warned against unrest, as police rounded up senior Islamists ahead of the planned Brotherhood protests.
The authorities have also closed the Rafah border crossing with Gaza for the day.
Army, led by General Abdel Fattah al-Sisi , released a statement later on Thursday on its Facebook page, saying that everyone had a right to peaceful protest, but that right should not be abused.
Excessive protests, the army warned, could lead to civil unrest, while reiterating that it was not targeting any political group.
"Wisdom, true nationalism and constructive human values that all religions have called for, require us now to avoid taking any exceptional or arbitrary measures against any faction or political current," the statement said.
Even the newly sworn-in interim leader Adly Mansour, who replaced Morsi as the president, used his inauguration on Thursday to heal the relationship with the Brotherhood.
"The Muslim Brotherhood are part of this people and are invited to participate in building the nation as nobody will be excluded, and if they respond to the invitation, they will be welcomed," he said.