Thousands of Egyptians have continued to occupy Cairo's Tahrir Square despite an offer from the military for a speedier handover to civilian rule.

After four days of violent clashes, Field Marshal Mohamed Hussein Tantawi said presidential elections would be held by July 2012.

But many protesters in the square said the concession was not enough and have demanded the field marshal step down.

Clashes continued throughout the night between police and protesters in Cairo.

Television pictures from Tahrir Square showed ambulances arriving to pick up injured people.

According to Egypt's ministry of health, at least 30 people have been killed since Saturday and hundreds injured.

Police have been using tear gas, rubber bullets and birdshot against protesters who have been throwing stones.

Some protesters said live bullets had been fired.

Clashes have also been reported in several other Egyptian cities including Alexandria, Suez, Port Said and Aswan.