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 Matthew Cassel, 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.
Also on Friday, Adly Mansour, the newly appointed interim head of state, dissolved parliament by decree, state television said.
Only the upper house, the Shura Council, had remained active after the lower house was dissolved by military-led authorities shortly before Morsi was elected a year ago.
State TV also said that Mansour had appointed Mohamed Ahmed Farid as head of intelligence. He replaces Mohamed Raafat Shehata, a Morsi appointee, who becomes national security adviser to Mansour.
In Nasr City in the Egyptian capital, thousands of supporters of Morsi gathered after Friday prayer to protest against his ouster.
The leader of Egypt's Muslim Brotherhood, Mohamed Badie, addressed the crowd saying that the protesters will continue their sit-in until Morsi is released.
"The Muslim Brotherhood are ones who have been serving you and I am one of your servants. The masses are here for God's religion first and for freeing Egypt," Badie said, adding; "We will stay in public squares until we free our elected president and we carry him on our shoulders."
The prosecutor's office ordered Badie's arrest on Thursday after the overthrow of Morsi, but Badie said that he was not detained. "Reports about my arrest are false. It is a lie. We are free revolutionaries," he said.
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 coalition on Thursday urged people to take part in a "Friday of Rejection" protest following weekly prayers. The call was seen as a test of whether Morsi still has a support base in the country, and how the army will deal with it.
Later on Friday a large crowd of Morsi supporters marched from Nasr City towards the Maspero state TV building and clashed with anti-Morsi protesters on the 6th October bridge in the centre of the capital.
Morsi, who was Egypt's first democratically elected president, belongs to the Muslim Brotherhood movement .
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.
The newly sworn-in interim leader Mansour 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.
In Pictures: What are Pro-Morsi protesters saying?