Protesters and soldiers threw rocks at each other over a barbed wire barricade near the defence ministry in Cairo on Friday, with several protesters injured, AFP reporters said.
Bleeding protesters were ferried away by motorbike by fellow demonstrators and ambulances rushed to the scene of the anti-military rally.
Islamist and secular protesters had gathered in Abbassiya near the defence ministry since the morning, separated from the army by the wire.
Some began to throw rocks at the military police, prompting troops to respond with water cannon, AFP reporters said.
Military police, holding their shields in one hand, picked up rocks from the ground and hurled them back at the protesters.
Soldiers charged forward and retreated several times from the wire barricade separating them from the protesters. A water cannon truck hosed the protesters several times before pulling away.
Thousands of anti-military protesters took to the streets in both Cairo and Alexandria, days after deadly clashes near the defence ministry raised tensions ahead of landmark presidential elections later this month.