A spokesman for the office of the interim president said that Mr. ElBaradei, a leader of the secular groups who opposed ousted President Mohammed Morsi, hadn't been appointed prime minister. The official state news agency had earlier reported that Mr. ElBaradei would be sworn in Saturday, sparking criticism from Islamist supporters of Mr. Morsi.
The spokesman, in a late night news conference broadcast on Egyptian state television, said discussions with various political parties were still under way over who would be appointed prime minister and help lead the transition following the military-led ouster of President Morsi.
When asked if opposition from the ultraconservative Salafi Nour Party had lead interim President Adly Mansour to withdraw the nomination of Mr. ElBaradei, the spokesman said no. He added that several people, including Mr. ElBaradei, were being considered for the post.
The spokesman, Ahmed al-Muslimani, said the erroneous report was a result of leaks to media. The Middle East News Agency reported that Saturday Mr. ElBaradei would be sworn in as interim prime minister later in the day. The Associated Press, citing a spokesman for the National Salvation Front, a secular coalition Mr. ElBaradei heads, said he had been chosen by Mr. Mansour.
Any appointment of Mr. ElBaradei would elevate him to a position in government for the first time since he entered the nation's political scene in 2010.
It would also come at a time of deep discord in Egypt after the Islamist President Morsi was removed from office by the military last week following street protests that drew millions demanding he step down. On Friday, at least 30 people were killed in fierce clashes between Mr. Morsi's supporters and opponents.
Tamarud, the newly founded youth movement that initiated the anti-Morsi protests on June 30 that ultimately led to Mr. Morsi's ouster, had chosen Mr. ElBaradei, a former diplomat and Nobel Prize laureate, as its representative.
Mr. ElBaradei was among the important Muslim, Coptic and opposition figures that stood with Defense Secretary Gen. Abdel Fattah Al Sisi as he announced Mr. Morsi's ouster last Wednesday. He said he supported the military's decision and their "road map" to "rectify the course of the revolution."
The reports of Mr. ElBaradei's nomination sparked frustration among Islamists on Saturday. The appointment of such a polarizing figure, so soon after the Islamists' humiliation at the hands of the military, appeared to some as salt on the Islamists' wounds.
"He's an agent of the West who has put foreign interests over Egyptian interests," said Mohammed al-Nashar, a Muslim Brotherhood leader in Damietta province. "He has a long history of hostility to Islamists. His enthusiastic support for the military coup and arrests of our leaders has shown that he does not really believe in democracy."
"This appointment and the military coup that brought him to power will take Egypt back to the Mubarak era," Mr. Nashar said.
The news sparked claims of hypocrisy.
"You criticize the Muslim Brotherhood and the Islamists for not sharing in their decision making, but then you do the same thing, but with a different approach," said Amr Mekki, a member of the Nour Party, the largest political group representing ultraconservative Salafi Islamists. "This isn't the way of democracy or the way of dealing with a country like Egypt like that," he said.
Mr. ElBaradei's ascent would put the Nour Party in an awkward position, navigating the post-Morsi landscape without being seen as compromising their Islamist roots should they support a transition led by a figure widely seen as an obstructionist to Islamist political aspirations.
"The Nour Party is important to this whole setup," said Michael Hanna, an Egypt expert at the New York-based Century Foundation. "There will be some consternation among the Nour Party and of course the Muslim Brotherhood."
Mr. Mansour on Saturday met with representatives of political parties, the military and the judiciary at the Presidential Palace in Cairo to begin planning how to implement the military's transition plan, which calls for an interim government to rule Egypt while an appointed committee drafts a new constitution and new elections are held.
The Muslim Brotherhood was invited to send a representative to the meeting, but refused, according to Mohammed Touson, a senior Muslim Brotherhood official who received the invitation.
"If we had agreed to meet with the president it would have meant we recognized the legitimacy of the military coup," Mr. Touson said. "The only legitimate president we recognize is Mohammed Morsi."
Those who attended the meeting included: Mr. ElBaradei; Court of Cassation Chief Justice Hamed Abdallah; Gen. Mamdouh Shaheen, a member of the Supreme Council of the Armed Forces; Abdel Moneim Aboul Fatouh, the former Muslim Brotherhood leader who quit the movement and ran for president as a moderate pro-revolution independent Islamist; a representative of the conservative Nour Party; and representatives of Tamarud.
Mr. ElBaradei, a former head of the head of the International Atomic Energy Agency, returned to Egypt in 2010 and became a vocal critic of then-President Hosni Mubarak. Since then, he has been an enigmatic figure—once leading the popular uprising that brought down Mr. Mubarak, only to shun public office afterward in protest of the military-led transition.
Mr. ElBaradei has developed a reputation as the principled dean of Egypt's political class—a respected, if somewhat withdrawn, voice of moral authority.
Yet he rarely grants interviews or makes public appearances. Even when he has engaged politically, both his supporters and opponents have criticized him for taking potshots from behind the ramparts of social media.
Mr. ElBaradei frequently weighs in on political events over his Twitter account—where he has 1.7 million followers—without actually making many public appearances.
He ranks among Egypt's more stubborn opposition leaders, having led calls to boycott parliamentary elections that had been planned for this fall while refusing to respond to Mr. Morsi's frequent calls for dialogue with the opposition.
Mr. ElBaradei has also emerged as one of the Islamists' strongest critics.
"Some would see this as a move that would only further infuriate the Muslim Brothers," said Mazen Hassan, an assistant professor of political science at Cairo University. "Not only has their democratically elected president been deposed but one of their fiercest enemies has been appointed prime minister."
"ElBaradei has never held an executive position in Egypt before," said Mr. Mazen. "He has certainly been the IAEA chief, but running the Egyptian government is different from any other organization."
Mr. Hanna, of the Century Foundation, described the task of attempting to unite Egypt's fractured political players as a "Kamikaze mission."
Still, he said, Mr. ElBaradei "is someone that lots of people, despite frustrations with him as a politician, believe has integrity."
The political turmoil came as a relative calm prevailed over the streets on Saturday.
Both sides continued to hold sit-ins and troops were in evidence on the streets. Debris from Friday's clashes littered the streets of downtown Cairo and its suburbs.
Friday's demonstrations made clear Islamists wouldn't quietly accept the military leaders' ouster of Mr. Morsi and deepened the rift between them and his critics.
The leadership of the Muslim Brotherhood, the organization of which Mr. Morsi was a prominent member and which propelled him to power last summer, had called for peaceful demonstrations to voice outrage over his removal, but sections of the protests descended into violence between his supporters and security forces, as well as street battles with protesters who called for Mr. Morsi's resignation.
Supporters of Mr. Morsi have vowed to stay in the streets until he is reinstated.
In a sign of just how much the current crisis has shifted Egyptians' focus, a court proceeding in a trial that once riveted the population passed Saturday with barely any notice. Mr. Morsi's predecessor, Hosni Mubarak, appeared in a Cairo court Saturday for a hearing in his retrial on charges of corruption and involvement during the 2011 popular uprising that lead to his ouster. The retrial was adjourned to Aug. 17.—Reem Abdellatif contributed to this article.
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