Egypt Crisis: Military on streets in Cairo to maintain security
Egypt's President Morsi has ordered the military to maintain security and protect state institutions in the run-up to a referendum on the constitution.
The army has also been given the power of arrest.
Mr Morsi has tried to calm public anger by annulling a decree giving him huge powers, but rejected a call to scrap the 15 December vote on a new constitution.
The BBC's Shaimaa Khalil is in Cairo.