Egypt's opposition has rejected an attempt by President Mohammed Morsi to end an increasingly bitter face-off.
Mr Morsi annulled a decree that gave him huge powers, but vowed that a vote on a new constitution would go ahead.
Opposition leaders rejected the move and called for protests on Tuesday. Later, Islamist groups said they would hold counter demonstrations.
The president's critics accuse him of acting like a dictator, but he says he is safeguarding the revolution.
In a statement after talks on Sunday, the opposition National Salvation Front said it would not recognise the draft constitution "because it does not represent the Egyptian people".
"We reject the referendum which will certainly lead to more division and sedition," spokesman Sameh Ashour said at a news conference.
The opposition says the body that drafted the constitution was dominated by Mr Morsi's Islamist allies.
In response, the Alliance of Islamist Forces, an umbrella group that includes Mr Morsi's Muslim Brotherhood, said it would hold rival demonstrations.
The group said its rallies would support of the referendum and the president under the slogan "Yes to legitimacy".
The situation is as tense as ever, says the BBC's Jon Leyne in Cairo.
He says the president has ordered the military to maintain security and protect state institutions in the run-up to the referendum, a move that will raise fears of a return to military rule.
The army has built a wall of concrete blocks to seal off and protect the presidential palace, which has been the focus of opposition demonstrations.
Earlier, Mohamed Soudan, foreign relations secretary of the Muslim Brotherhood's Freedom and Justice Party, said Mr Morsi was constitutionally bound to go ahead with the vote.
Mr Morsi's decree of 22 November stripped the judiciary of any right to challenge his decisions and triggered violent protests in Cairo.
Although the decree has been annulled, some decisions taken under it still stand.
The general prosecutor, who was dismissed, will not be reinstated, and the retrial of the former regime officials will go ahead.
The president's supporters say the judiciary is made up of reactionary figures from the old regime of strongman Hosni Mubarak.
Egypt's powerful military has warned it will not allow Egypt to spiral out of control and has called for talks to resolve the conflict.
But his opponents have mounted almost continuous protests since the decree was passed.
Several people have been killed in the recent spate of protests on both sides, and the presidential palace has come under attack.
The Cairo headquarters of the Muslim Brotherhood, the movement to which Mr Morsi belongs, were set on fire.