Security officials say suspected Islamists have killed three protesters in the southern city of Assiut, taking to four the number of people killed on a day of massive protests demanding the ouster of Egypt's president.

The officials said Islamists on a motorbike opened fire on protesters outside the local government building in Assiut, killing one and wounding seven. Enraged by the killing, protesters marched to the office of the Freedom and Justice party, political arm of President Mohammed Morsi's Muslim Brotherhood.

Gunmen inside the building opened fire, killing at least two, according to the officials, who spoke on condition of anonymity because they were not authorized to speak to the media.

A protester in Beni Suef was killed earlier outside the local headquarters of the Freedom and Justice party.