Egypt is bracing for rival protests to take place in Cairo on Tuesday over a bitterly divisive referendum on a new constitution, AFP reported on Monday.
The situation prompted President Mohammed Morsi to order the army to help "preserve security,” the report said.
The dueling demonstrations, organized by Islamists backing Morsi and the largely secular opposition, raised fears of street clashes like ones last week in which seven people were killed and hundreds injured.
Morsi's decree instructing the military to fully cooperate with police "to preserve security and protect vital state institutions for a temporary period, up to the announcement of the results from the referendum" came into force on Monday.
Army officers "all have powers of legal arrest," it says, according to AFP.
The military, which has urged dialogue and warned it "will not allow" the political crisis to deteriorate, has for several days kept tanks and troops deployed around Morsi's presidential palace.
Late Monday, soldiers merely watched as more than 100 anti-Morsi demonstrators milled around in front of the palace, AFP reported.
The opposition, made up of secular, liberal, leftwing and Christian groups, has said it will escalate its protests to scupper the referendum.
The main opposition group, the National Salvation Front, has called for huge protests in Cairo to reject the constitutional referendum, which is scheduled for Saturday.
The Muslim Brotherhood, from which Morsi hails, said Islamist movements would counter the protests with their own big rallies in the capital in support of the referendum.
"We are calling for a demonstration Tuesday, under the slogan 'Yes to legitimacy'," the Brotherhood's spokesman, Mahmud Ghozlan, told AFP.
A group of senior judges on Monday said pro-Morsi Islamist protesters would have to lift a week-long sit-in outside the constitutional court before they would consider overseeing the referendum.
If the charter is rejected, Morsi has promised to have a new one drawn up by 100 officials chosen directly by the public rather than appointed by the Islamist-dominated parliament.