A deadly gunfight erupted in Cairo on Friday as thousands of supporters of deposed Egyptian president Mohamed Morsi marched on the Republican Guard headquarters during mass rallies against the Islamist's ouster.
An AFP correspondent said at least three people were killed and many others wounded as shooting broke out after thousands of Islamist demonstrators approached the headquarters chanting "traitors" and "Morsi is our president".
The bodies of two people were covered with sheets, said the correspondent, adding that another protester was shot in the head and fell to the ground, parts of his brain spilling from his skull.
The Islamists had streamed towards the Guards headquarters on foot from a Muslim Brotherhood rally that attracted tens of thousands at Cairo's Rabaa al-Adawiya mosque.
They accuse the military of conducting a brazen coup on Wednesday against Morsi, Egypt's first democratically elected president, after millions called for his ouster on the June 30 anniversary of his first turbulent year in power.
Shortly before Friday's rallies, around a dozen low-flying military jets screeched across Cairo, a day after warplanes had left a heart-shaped trail of smoke in the sky.
The show of force failed to deter Morsi's supporters, however.
Shots rang out after one Morsi supporter tried to hang a picture of the ousted leader on barbed wire outside the headquarters, said the AFP correspondent.
He was warned twice by members of the Republican Guard not to approach the building before they started shooting.
Gunfire could then be heard from both directions, and security forces also later used tear gas.
Morsi, who has not been seen since Wednesday, had issued a defiant call for supporters to protect his elected "legitimacy", in a recorded speech aired hours after his removal.
The military had said it supported the right to peaceful protest, but warned against violence and acts of civil disobedience such as blocking roads.
Armed forces were also on high alert in the restive Sinai peninsula, bolstering security after Islamist militants killed a soldier in a machinegun and rocket attack.
Clashes also broke out in the Nile Delta province of Sharqiya, hours after chief justice Adly Mansour, 67, was sworn in as interim president until new elections.
Mansour called for unity in an interview broadcast on the eve of Friday's rallies.
"All I can say to the Egyptian people is to be one body. We had enough of division," he told Britain's Channel 4 television.
"The Muslim Brotherhood is part of the fabric of Egyptian society. They are one of its parties. They are invited to integrate into this nation and be part of it."
Prominent liberal leader Mohamed ElBaradei defended the military's intervention.
"We asked the army to intervene because the other option was a civil war. We were between a rock and a hard place, and people need to understand that," the former UN nuclear watchdog chief told the BBC.
Army chief General Abdel Fattah al-Sisi announced Morsi's overthrow on Wednesday night, citing his inability to end a deepening political crisis, as dozens of armoured personnel carriers streamed onto the streets of the capital.
Military police have since arrested Brotherhood supreme leader Mohammed Badie "for inciting the killing of protesters", a security official told AFP.
Former supreme guide Mahdi Akef was also arrested, state television reported.
Morsi himself was "preventively detained" by the military, a senior officer told AFP hours after his overthrow, suggesting he might face trial.
A judicial source said the prosecution would on Monday begin questioning Brotherhood members, including Morsi, for "insulting the judiciary". Thirty-five of them have been banned from travel.
But controversial public prosecutor Abdel Meguid Mahmud said Friday he was to resign, days after being reinstated, citing possible conflicts of interest in future prosecutions.
Morsi supporters argue the president was confronted at every turn with a hostile bureaucracy left over by former strongman Hosni Mubarak, overthrown in the country's 2011 uprising.
Morsi's rule was marked by a spiralling economic crisis, shortages of fuel and often deadly opposition protests.
US President Barack Obama said he was "deeply concerned", but refrained from calling the military intervention a coup.
In May, Washington approved $1.3 billion in military aid to Egypt. That was now under review, said Obama, as he called for a swift return to democratic rule.
The African Union suspended Egypt in response to Morsi's ouster, after Middle Eastern governments welcomed the military's intervention in varying degrees, with war-hit Syria calling it a "great achievement".