Thousands of supporters of deposed Egyptian President Mohammed Mursi rallied in Cairo today to demand the restoration of the ousted Islamist leader.
His opponents were planning protests nearby.
Two formations of fighter jets passed over the city after noon prayers ended.
Four army helicopters circled, while another five, trailing Egyptian flags, flew low over Cairo roof tops, in a clear show of strength by the military.
More than two weeks after Egypt's powerful military removed Mr Mursi from office, there was still no sign of a possible deal to defuse the crisis.
The Muslim Brotherhood has called for demonstrations around the country, accusing the head of the armed forces, General Abdel-Fattah al-Sisi, of staging a coup to force Egypt's first freely-elected president from power.
The army said it had to intervene after mammoth street protests against Mr Mursi, who was criticised as incompetent and partisan, and has installed an interim cabinet to prepare for elections.
It includes no members of Mr Mursi's Muslim Brotherhood or other Islamist parties previously in government.
Mursi supporters have set up a round-the-clock vigil outside a mosque in the Cairo suburb of Nasr City.
Thousands flocked there today to join protests that swelled after noon prayers.
"Tonight, tonight, tonight, Sisi is going down tonight," a man shouted out, leading the chants.
A huge banner showed a picture of Mr Mursi against Egyptian flags and read: "Together to support legitimacy."
Scuffles broke out when Mursi supporters began chanting against General Sisi, the army chief, after prayers near al-Azhar mosque in central Cairo, security sources said.
Police fired shots in the air to disperse them and arrested two Brotherhood supporters after they fought opponents with fists and rocks, they said. No casualties were reported.
Egypt's closest western ally, the United States, has tried to tread softly through the crisis, still undecided whether to brand the downfall of Mr Mursi a military coup.
That would force the US to suspend its large aid programmes for Cairo.