Egyptian troops fired tear gas at anti-military protesters on Friday and both sides hurled rocks at each other, as tensions spiraled ahead of landmark presidential elections.

A blanket of thick smoke engulfed Abbassiya square near the defence ministry in Cairo, days after deadly clashes there that prompted Friday's demonstration.

Bleeding protesters were ferried away by motorbike and ambulances rushed to the scene, an AFP reporter said. State television showed several soldiers wounded.

The clashes began when some protesters threw rocks at the military police, prompting troops to respond with water cannon and then eventually tear gas.

Military police, holding their shields in one hand, picked up rocks from the ground and hurled them back at the protesters, who used metal sheets from nearby construction sites to protect themselves. [AFP]