The protesters, mainly from the influential Muslim Brotherhood and radical Salafists, are angry at a decision by the election commission to allow Ahmed Shafiq, who was appointed premier in Mubarak's final days in power, to run in the May 23-24 election.

The commission said Thursday Shafiq had been reinstated after filing an appeal against an earlier disqualification.

Thirteen contenders, including three Islamists, are to compete in the vote, Egypt's first since Mubarak's overthrow in February 2011.

Supporters of Salah Abu Ismail, a populist Salafist, joined the demonstration to protest his exclusion from the presidential race.

The election commission said it had proof his mother had acquired a US passport.

Abu Ismail's followers have been on a strike for more than a week in Tahrir Square, the focal point of mass protests that forced Mubarak to resign last year.

The protesters chanted slogans against the generals who have taken over after Mubarak, and demanded that they transfer of power to civilians.

Banners hung across the square read: "No to election under the military rule," and "No to candidates from the former regime."