Tensions are rising among supporters of deposed Egyptian president Mohamed Morsi amid reports that security forces are preparing to move against two protest camps in Cairo.
Western and Arab mediators and some senior members of the Egyptian government have been trying to persuade the army to avoid using force to disperse the protesters, fearing a new wave of bloodshed.
International news agencies are quoting unnamed Egyptian officials saying forces would begin to surround the camps on Monday.
Egypt's interim leaders had warned several times they would dismantle the sit-ins after the Eid al-Fitr holiday which ran through Sunday.
Senior government sources told the pan-Arab Asharq Al-Awsat newspaper the plan will be carried out gradually in an attempt to keep casualties among Mr. Morsi's supporters to a minimum.
A brief power cut early Sunday at the main sit-in outside the Rabaa al-Adawiya mosque struck panic among the pro-Morsi demonstrators.
"They are warning us by cutting electricity power and the media said today that there will be one hundred and twenty riot police units that will be deployed to end the sit-ins in Rabaa and al-Nahda. Even if they brought millions of riot police units, it would make no difference: we are ready to die here," said pro-Morsi protester Nabil Ahmed Shahin.
The government later issued a statement saying the blackout at Rabaa al-Adawiya in northeast Cairo was unintentional.
Many protesters, expecting an imminent security push to clear them out, have begun fortifying their positions.
Vendors at Rabaa al-Adawiya have sold hundreds of gas masks, goggles and gloves to protesters readying themselves for police tear gas. Cement and wooden barriers have been constructed by protesters to keep armored vehicles from crushing the sit-in.
Pro-Morsi supporters have said they will not leave the sit-ins until the president, ousted in a popularly supported coup July 3, is reinstated.