"The constitutional decree is annulled from this moment," former presidential candidate Mohamed Selim El-Awa told a press conference in Cairo late on Saturday night, Press TV reported.
A referendum on a draft constitution will still go ahead as planned on December 15, he added.
But opposition factions, uncertain of their ability to vote down the constitution against the Islamic groups’ organizational muscle, want the document redrafted before any vote.
Ahmed Said, a liberal leader of the main opposition National Salvation Front, said Morsi's withdrawal of his November 22 decree had not annulled its consequences, describing the race to a referendum as "shocking" and an "act of war" against Egyptians, Reuters reported.
The Front had promised a formal response later on Sunday.
Earlier on Saturday, Egyptian Prime Minister Hesham Qandil told an Egyptian television channel that Morsi was preparing to amend the decree.
The Egyptian president tasked six officials and elements of the opposition to "modify the constitutional declaration" he issued last month, Qandil said.
The officials, including politicians and members of the judiciary, "met to draft a new text (decree) and could finalize it late on Saturday or on Sunday morning," he added.
On November 22, Morsi issued a decree declaring that no judicial body could dissolve the Constituent Assembly, which was writing the draft of the constitution.
The decree allowed the president to take "any decision or measure to protect the revolution." It also made decisions and laws drafted by the president "final and not subject to appeal."
Since November 22, tens of thousands of Egyptians have held demonstrations across the country against and in support of the draft constitution, which stated that the nation would be governed by the principles of Islamic law.
On November 30, the Constituent Assembly approved the final draft of the new constitution.
On December 1, the Egyptian president announced that a referendum on the new constitution would be held on December 15, 2012.
Morsi's office issued a statement on Saturday, saying that the president had opened his "national dialogue" with about 40 political and other public figures to discuss "means to reach a solution to differences over the referendum… and the constitutional decree."
The Egyptians launched a revolution against the pro-Israeli regime in January 2011, which eventually brought an end to the 30-year dictatorship of former President Hosni Mubarak in February 2011.
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