Pro-reform leader Mohamed ElBaradei's candidacy for Egypt's interim premiership has been challenged by some Islamists who say the move would heighten polarisation between opponents of toppled president Mohamed Morsi and his Islamist backers.
The Rebel ('Tamarod') campaign, which spearheaded the 30 June protests that culminated in Morsi's overthrow, condemned on Sunday what it called the presidency's "back-tracking" on his choice of ElBaradei and voiced premature rejection to any alternative candidate.
MENA state news agency said on Saturday that Egypt's Interim President Adly Mansour had named the Nobel Prize laureate as prime minister, only to later deny that a final decision had been taken on the matter.
Rebel spokesman Mahmoud Badr said the campaign should have been consulted by the presidency before other names were brought to the table.
Badr went on to say his movement would not "recognise" or "deal with" any premier other than the staunch democracy advocate.
ElBaradei's nomination, which delighted opponents of toppled president Mohamed Morsi, was opposed by the Salafist Nour Party, who has also thrown its weight behind the army-led "roadmap" following Morsi's Wednesday ouster.
The ultra-conservative party said ElBaradei's appointment would widen the rift in an increasingly polarised county.
A key anti-Morsi coalition led by Rebel reiterated its backing of the former UN nuclear watchdog head's nomination
The 30 June Front slammed what it perceived as pressure from Egypt's second-largest Islamist group on the presidency's choice of ElBaradei.
The front said it rejected any conditions dictated by the Nour Party, in addition to what it described as some parties' attempts "to have the upper hand" on the people.
Nour Party vice chairman Bassem El-Zaraka said his party would withdraw from the political transition process if ElBaradei was confirmed as prime minister.
"We are not exclusionary... but we won't allow the replacement of the Brotherhood with the Salafists" the 30 June Front said on Sunday.
The group claimed that ElBaradei's appointment had consensus across the political spectrum and amongst the revolutionary youth.
Within minutes after the news broke that ElBaradei would be named premier, a senior Brotherhood official said that the Islamist movement would reject his candidacy and any other measures implemented by the army-backed administration.
"We reject this coup and all that results from it, including ElBaradei," Farid Ismail, of the Brotherhood's political wing the Freedom and Justice Party (FJP), told Reuters.
A Brotherhood-led coalition called for another wave of protests on Sunday, heightening fears of further violence which has brought fresh unrest in Egypt since Morsi's ouster.
Newly-appointed presidential media advisor Ahmed El-Moslemani stressed on Sunday, however, that ElBaradei remained a "strong contender."
"There are several choices and it is logical that ElBaradei is the first choice of the revolutionary youth. But there are other forces that have been proposing other candidates," the media advisor said.