President Mohammed Morsi's decision to fire a hard-line Islamist as an adviser has laid bare rivalries between Egypt's two biggest Islamist groups as parliamentary elections approach.
The sacking of Khaled Alameddin of the Salafi Nour Party on Sunday has led his movement to step up criticism of the Muslim Brotherhood that propelled Mr. Morsi to office, narrowing the already slim chances of the two movements working together in the election.
Mr. Alameddin broke down in tears during a news conference on Monday, saying he had been accused of abusing power. The presidency has yet to issue a statement on why Mr. Alameddin was dismissed.
"I formally demand an apology from the President. I won't accept an apology less than that," Mr. Alameddin said. Another of Mr. Morsi's advisers from the Nour Party, Bassam El-Zarka, announced his resignation at the news conference, apparently in solidarity with Mr. Alameddin.
The Nour Party, which emerged from the ultra-conservative religious movement Daawa Salafiya, came second to the Muslim Brotherhood in Egypt's last parliamentary elections, the results of which were overturned by a court ruling last June. New elections are due to begin in April or May.
Mr. Morsi employed several Nour Party members as advisers. The groups co-operated to drive through an Islamist-tinged constitution approved in a December referendum, deepening a national divide between Islamists and their opponents.
But, in recent weeks, the Nour Party has sought to distance itself from the Brotherhood, whose popularity has been dented by a deepening economic crisis and a standoff with political rivals who say it wants to monopolize the institutions of state.
The Nour Party did not take part in a pro-Morsi rally called last Friday by another hard-line Islamist party.
"The Brotherhood has become more radioactive from the Nour Party's standpoint now," said Shadi Hamid, director of research at the Brookings Doha Center. "They [Nour] want to present themselves as the pure Islamic alternative."
Nour has sought to defuse tension between Mr. Morsi's presidency and Egypt's liberal and leftist opposition, an apparent attempt to burnish its image as a responsible, mature political player.
The Brotherhood's Freedom and Justice Party has poured cold water on the initiative.
The FJP, which won about 40 per cent of seats in the last elections, said last week it aimed to secure an outright majority in the next parliament.
Nour Party spokesman Nader Bakkar said Mr. Alameddin had been dismissed without proper investigation, and took a stab at Mr. Morsi over accusations that his family had recently benefited from connections by securing state employment for one of his sons.
A media furor over the appointment of Omar Morsi at a firm affiliated with the Civil Aviation Ministry forced him to forgo the job on Sunday.
Mr, Hamid said there was no "natural affinity" between the two Islamist groups. "There has always been a tense relationship," he said.