President Mohammed Mursi has ordered Egypt's army to take on police powers - including the right to arrest civilians - in the run-up to a divisive constitutional referendum that has triggered mass street protests.
The decree, published in the government gazette, takes effect on the eve of mass rival protests on the referendum and follows street clashes that have left seven people dead and hundreds injured.
It orders 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", according to the decree.
The military, which ruled Egypt between the ousting of former president Hosni Mubarak in February 2011 and the election of Mursi in June this year, has sought to remain neutral in the political crisis.
It has warned it "will not allow" the situation to deteriorate, and urged both sides to dialogue.
Army tanks and troops have since Thursday deployed around Mursi's presidential palace but they have not confronted thousands of protesters who have gathered there every night.
The opposition, made up of secular, liberal, left wing and Christian groups, has said it will escalate its protests to scupper the referendum.
It views the draft constitution, which was largely drafted by Mursi's Islamist allies, as undermining human rights, the rights of women, religious minorities and curtailing the independence of the judiciary.
Mursi, though, has defiantly pushed on with the new charter, seeing it as necessary to secure democratic reform in the wake of Mubarak's 30-year autocratic rule.
Late Sunday, the main opposition group, the National Salvation Front, called for huge protests in Cairo to reject the December 15 referendum.
It dismissed a key concession Mursi made, rescinding another decree giving himself near-absolute powers, as too late, saying he had already used it to railroad through the draft constitution.
"We do not recognise the draft constitution because it does not represent the Egyptian people," National Salvation Front spokesman Sameh Ashour said.
Going ahead with the referendum "in this explosive situation with the threat of the Brothers' militia amounts to the regime abandoning its responsibilities", he said.
The Muslim Brotherhood shot back that it, along with allied Islamist movements, would counter with their own big rallies.
Mursi's camp argues it is up to the people to accept or reject the draft constitution.
If the charter is rejected, Mursi 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.