Five people have been killed by unknown assailants at a protest near the Egyptian defence ministry building in the capital, Cairo, officials say.
Up to 100 people were also reportedly injured and are being treated at a field clinic in the Abbasiya district.
Many of the protesters are supporters of a Salafist preacher barred from standing in the presidential election.
Activists accuse the ruling military council of using thugs and plainclothes troops to break up demonstrations.