Egypt's electoral commission has confirmed that ten candidates have been barred from running for president.
The move rules out a challenge by two Islamists and Hosni Mubarak's ex-spy chief.
Among the candidates still able to run are former Arab League chief Amr Mussa and Abdelmoneim Abul Futuh, a former
member of the powerful Muslim Brotherhood.
The commission had held a day-long meeting to hear appeals from disqualified candidates, including former spy chief Omar Suleiman.
The electoral commission said Saturday it had rejected the candidacy of the ten due to irregularities in their applications.
Although expected in some quarters, the news of the decision threw the presidential campaign into turmoil as the fate of a new constitution remains hanging in limbo.
The Muslim Brotherhood had anticipated the decision by putting up Mohammed Morsi, chairman of the movement's Freedom and Justice Party (FJP), as an "alternative" candidate.
The Muslim Brotherhood's Khairat El-Shater, who was in jail last year on charges of terrorism and money laundering, was barred because of a law stating candidates can only run in elections six years after being released or pardoned.
The Brotherhood's Twitter feed quoted Mr Shater as saying "my exclusion from the presidential race despite sound legal case is a proof Mubarak is still in power. We shall continue in our peaceful struggle to complete our unfinished revolution."
Later addressing hundreds of partisans in Cairo, Mr Shater - a wealthy businessman - called on Egyptians to "protect the revolution," warning that plans for electoral fraud and vote-buying were under way.
He promised "to topple the remains of the Mubarak regime."
Mr Suleiman was disqualified because he failed to garner enough endorsements from all 15 provinces as required under the law.
Popular Salafist politician Hazem Abu Ismail is out of the race because his mother holds foreign nationality, violating election rules which state that all candidates, their parents and their wives must have only Egyptian citizenship.
The latest developments in the presidential campaign further complicate the transition to democracy after former president Mubarak was ousted last year.
They come a week after a Cairo court suspended the Islamist-dominated commission tasked with drafting a new constitution amid a boycott by liberals, moderate Muslims and the Coptic church.
The panel, which is evenly divided between parliamentarians and public figures, was elected by the parliament.
But most of its members were from the Muslim Brotherhood and Salafist fundamentalists who hold the majority in both houses of parliament.
Secular parties withdraw from commission
The secular parties had already withdrawn from the commission, believing their presence was only used as a smoke screen allowing the Islamists to draft a basic law reflecting their ideologies.
The prestigious Sunni Islamic institution, Al-Azhar, and the Coptic Orthodox Church of Egypt have also boycotted the panel.
Islamists believe the commission should reflect the composition of a parliament where the FJP holds nearly half the seats and the Salafist Al-Nur party almost one quarter.
The secularists want a more balanced commission, fearing the Islamist grip would lead to the strengthening of a demand for Islamic sharia law to be the point of reference for legislation.
In principle, the panel has up to six months to draft a new constitution to replace the one suspended by the military when it took power last year.