Rival mass protests have been called for next Tuesday in Egypt over a bitterly disputed constitutional referendum, raising the potential for more violent street clashes in a sharpening political crisis.
President Mohamed Morsi's chief foes, the opposition National Salvation Front, late Sunday called for huge protests in Cairo to reject the December 15 referendum on a new charter.
The Muslim Brotherhood, from which Morsi hails, told AFP that it and allied Islamist movements would counter with their own big rallies in the capital in support of the referendum.
If the duelling demonstrations go ahead, there is a risk of vicious further clashes like the ones that erupted between both sides outside the presidential palace last Wednesday, killing seven people and wounding hundreds.
Egypt's powerful army, which is trying to remain neutral in the deepening struggle, warned on the weekend it "will not allow" a worsening of the crisis. It said both sides must start dialogue.
Morsi has made a key concession to the opposition on the weekend by rescinding a decree giving himself wide-ranging powers free from judicial challenge.
But the opposition was unmoved, and maintained its position that no talks could happen while the referendum was going ahead.
"The Front calls for demonstrations in the capital and in the regions on Tuesday as a rejection of the president's decision that goes against our legitimate demands," National Salvation Front spokesman Sameh Ashour told a news conference.
"We do not recognise the draft constitution because it does not represent the Egyptian people," he said, reading a statement.
Going ahead with the referendum "in this explosive situation with the threat of the Brothers' militias amounts to the regime abandoning its responsibilities," he said.
The Brotherhood's spokesman, Mahmud Ghozlan, told AFP that the Alliance of Islamist Forces it belongs to was also "calling for a demonstration Tuesday, under the slogan 'Yes to legitimacy'," and in support of the referendum.
The almost nightly protests over the past two weeks have brought out thousands of people into the streets.
In recent days, the protesters have hardened their slogans, going beyond criticism of the decree and the referendum to demand Morsi's ouster.
Amid the protests and tensions, the army was watching nervously. Tanks and troops have been deployed outside the presidential palace but they have made no move to confront the demonstrators.
On Sunday, air force F-16 warplanes flew low over the city centre. The official MENA news agency described the unusually low flyover as an exercise against "hostile air attacks and to secure important state installations."
That did not prevent several hundred anti-Morsi protesters gathering outside his palace late Sunday, according to an AFP correspondent there.
The opposition sees the constitution, which was largely written up by Islamists, as a tool weakening human rights, the rights of women, religious minorities, and the judiciary's independence.
It dismisses arguments by Morsi aides that the referendum could not be delayed under constitutional rules requiring a plebiscite two weeks after it is formally presented to the president.
"The two-week deadline is just a date for organising the referendum, and you can postpone it without any problems," a Front leader, Munir Fakhri, told AFP.
Morsi's camp, though, argues that it is up to the people to accept or reject the draft constitution.
If it is rejected in the referendum, Morsi has promised to have a new one drawn up by 100 officials chosen by the public, rather than by the Islamist-dominated parliament as was the case for the current text.
Prime Minister Hisham Qandil has urged protesters from both sides to stop demonstrating, and to vote in next Saturday's referendum, MENA said.
Analysts said still-strong public support for Morsi, and the proven ability of his Muslim Brotherhood to mobilise Egypt's voters at the grassroots level, would likely help the draft constitution be adopted.
"The Muslim Brotherhood believes that it has majority support so it can win the constitutional referendum," said Eric Trager, analyst at the Washington Institute for Near East Policy.
If that happens, he warned, it would "set up the country for prolonged instability."