Egypt crowds fill Tahrir square http://bbc.in/HXi2cV
Egyptian protesters fill Cairo's Tahrir Square
The BBC's Jon Leyne says the demonstrations are probably the biggest in Tahrir Square since November
Many are angry at the disqualification of popular presidential candidates.
The first presidential poll since Hosni Mubarak was ousted from power last year is due to be held next month.
'Hijacking revolution'When the military took power it promised only to hold power until the election results were announced in June.
However, critics accuse it of not being committed to reform and of trying to stay in control through a proxy leader.
Some protesters in Tahrir Square chanted: "In Syria, the people are besieged by Bashar Assad and here we are besieged by Egypt's military rulers".
Islamist groups decided to back the rally, in part because of the recent barring of two prominent Islamist presidential hopefuls.
Khairat al-Shater had been the candidate for the powerful Muslim Brotherhood's Freedom and Justice Party, but was disqualified due to a conviction under the Mubarak era.
Popular ultra-conservative Salafi preacher Hazem Abu Ismail was barred because his mother allegedly held a US passport.
Their supporters accuse the ruling generals of "hijacking" the revolution.
Omar Suleiman, a former intelligence chief and ally of Mr Mubarak, was also deemed ineligible.
Mr Mubarak, who was forced out in February 2011 amid mass demonstrations, is being detained in a military hospital awaiting a verdict in a corruption and murder trial
