Egyptian security forces have fortified their presence around the capital and in neighbouring Giza ahead of planned demos called for against the interim authorities by supporters of ousted president Mohamed Morsi.

Despite a harsh crackdown by authorities on Islamists, the National Alliance to Support Legitimacy, a coalition led by Morsi's Muslim Brotherhood has called for a new round of protests on Friday, a usual day of protest in Egypt, to mark six months since a deadly police raid on pro-Morsi protest camps in Cairo which left hundreds dead.

Authorities deployed armoured vehicles and riot police early on Friday in the vicinity of Tahrir Suare, epicentre of mass protests that toppled autocrat Hosni Mubarak in 2011, state news agency MENA reported.

Army and police forces erected barricades and barbed wire around other volatile sites, including the Rabaa Al-Adawiya thoroughfare and the Ittihadeya presidential palace in Heliopolis district, eastern Cairo.

A crackdown by authorities on Morsi's supporters since his ouster has reduced the size of street protests. Thousands of supporters of the deposed leader have been arrested and hundreds killed in street violence.  

The government in December branded his Muslim Brotherhood group a terrorist organisation, linking the group with ongoing terrorist violence in Sinai and elsewhere in Egypt which has left dozens of security forces personnel dead. Brotherhood leaders have denied all links with the violence.

The interior ministry has said that taking part in Brotherhood protests or promoting them verbally or in writing could lead to harsh jail sentences.