Thousands of people rallied in central Cairo on Friday in support of a Salafist candidate who could be ruled out of Egypt's presidential election because his mother reportedly held US nationality.
Under the country's electoral law, all candidates for the presidency, their parents and their wives must have only Egyptian citizenship.
"The people want Hazem Abu Ismail! No to manipulation!" the demonstrators shouted after making their way through central Cairo to Tahrir Square, epicentre of last year's revolt which toppled president Hosni Mubarak.
The protesters, including women in full Islamic veil, carried portraits of Abu Ismail and waved their fists, angrily condemning any attempt to disqualify their candidate.
Abu Ismail launched his candidacy on March 30 with a large motorcade that took him to electoral commission headquarters in Cairo.
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Commission chief Hatem Begato said on Thursday that the agency had received information according to which Ismail's mother had "used an American passport for travel to and from Egypt" before her death.
Files will be examined on April 12-13 and any candidate not meeting the requirements informed, the commission said. Those rejected would then have 48 hours to appeal before the final list of candidates is announced on April 26.
Abu Ismail advocates a strict interpretation of Islam similar to the one practised in Saudi Arabia and has become a familiar sight in Cairo, with his posters adorning many cars and micro buses.
The May election will mark the beginning of a handover of power by the ruling military to an elected civilian leader, following the popular uprising against Mubarak.
Abu Ismail would compete with more moderate Islamist candidates such as senior Muslim Brotherhood figure Khairat El-Shater as well as former regime figures such as Amr Mussa, an ex-foreign minister.
Islamists have made big strides since Mubarak's ouster, winning majorities in elections to both houses of parliament.
The Muslim Brotherhood's Freedom and Justice Party won the most seats in parliamentary elections earlier this year, but the Salafists captured nearly a quarter themselves.