Tens of thousands of people rallied in Cairo's Tahrir Square on Friday to protest against the ruling military and hold-overs from the regime of former president Hosni Mubarak.
The demonstration comes ahead of the first presidential election since the strongman's ouster last year, to be held at the end of May.
Liberal groups had already called for the rally when, last week, the committee overseeing the election barred Mubarak's vice president and spy chief Omar Suleiman and two leading Islamist candidates from standing.
Islamists, who swept parliamentary elections earlier this year, held a rally with similar demands in the iconic square last week that was avoided by many liberal groups, highlighting rifts since the uprising.
But the powerful Muslim Brotherhood, whose political arm dominates both houses of parliament, said it would throw its weight behind Friday's protest after its candidate, Khairat El-Shater, was disqualified.
Supporters of disqualified Salafist candidate Hazem Abu Ismail also joined the protest, carrying black flags emblazoned with Islamic slogans.
Abu Ismail was barred because his late mother held joint US-Egyptian citizenship and the electoral law requires that candidates, their wives and parents have only Egyptian nationality.
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"Down with military rule," chanted the protesters in the square, epicentre of the 18-day revolt that overthrew Mubarak in February 2011 and left the military in power.
Thousands also marched into Tahrir Square after Friday prayers in several mosques around Cairo.
Suleiman, whom Mubarak appointed as vice president in the last days of his regime, was barred because he did not gather enough endorsements from across the country, as the electoral law requires.
His candidacy shocked the Brotherhood, which said it would escalate street protests if he continued to stand, and the parliament it dominates rushed through a law to bar former regime figures from the election.
The Islamists accused the military of backing Suleiman and claimed that security services had helped to gather the 30,000 endorsements he needed to nominate himself.
The military has promised to hand over power to a civilian president after the election results are announced in June, but its critics accuse it of angling to stay in power through a proxy leader.
Ahmed Shafiq, a former air force chief who served as Mubarak's prime minister, is still in the race, as is Amr Mussa, a former Mubarak foreign minister and Arab League chief.
The Brotherhood is fielding Mohammed Mursi, leader of its political wing the Freedom and Justice Party, after the electoral committee disqualified Shater because of a military court conviction during the Mubarak era.