The Egyptian army has tightened security in Cairo and other cities in response to the Muslim Brotherhood's calls for marches from 28 mosques following Friday prayers.
The group's call came a day after hundreds of people were killed in police action that ended two sit-ins in Cairo that began after the army deposed President Mohamed Morsi on July 3.
Al Jazeera sources said the military forces closed off entrances and exits and roads leading to Cairo's Tahrir Square with armoured personnel carriers and barbed wire.
|Map showing places where curfew has been in force
The Anwar Sadat metro station in Tahrir Square was shut down as a precautionary measure.
Security forces also closed off all streets leading to Rabaa al-Adawiya mosque.
Armoured personnel carriers had been deployed in several places in central Cairo.
Egyptian state TV reported that the military had deployed troops to guard what it described as vital installations.
Army commanders gave warning that troops would fire at anyone who attacked government buildings.
The Interior Ministry ordered its forces to use live ammunition when dealing with any attacks on security forces or building institutions, citing its legal right to defence.
"In light of the Muslim Brotherhood's targeting of some police and state institutions in several cities, the law permits policemen to use measures to secure the national and stop attacks on citizens and public and private property," the ministry said on its Facebook page on Thursday.
All forces in charge of securing and guarding these vital facilities were supplied with arms and vital facilities to abort any attack against them, the statement added.
The Muslim Brotherhood has dubbed the day "Friday of rage", which was the same title given on January 28, 2011, during the 18-day revolt against Hosni Mubarak's rule.
The Health Ministry said that at least 578 people and 46 police officers were killed in the clearing and subsequent clashes nationwide on Wednesday, with more than 3,500 were injured.
Muslim Brotherhood members have said the true death toll was far higher, with a spokesperson saying 2,600 people had been killed in the "massacre".
The interim government has defended the crackdown, saying authorities had no choice but to act.
Residents say they are tired of the violence. The state of emergency is set to run for a month.