The Egyptian army is warning supporters of ousted President Mohamed Morsi to stay away from military facilities, especially military intelligence headquarters.
An army statement calls these vitally important and secure installations. It says anyone approaching them would be in danger.
The warning comes after reports that Muslim Brotherhood members were planning to march on a military building in Cairo. The marchers are defying government warnings that it will break up protests and sit-ins against the president's ouster.
Thousands of pro-Morsi loyalists stood their ground Sunday outside the Raba'a al-Adawiya mosque and near Cairo University - one day after clashes with security forces killed at least 74 people and wounded 800.
European Union foreign policy chief Catherine Ashton is in Cairo for talks with Egyptian interim leaders. It is her second visit to Egypt in a month.
Morsi's Muslim Brotherhood movement said police and armed men opened fire Saturday when protesters tried to expand their sit-in camp by moving onto a nearby main avenue outside the mosque.
Egyptian officials deny the accusations, saying that police only fired tear gas and that pro-Morsi marchers were responsible for the violence.