Tens of thousands of protesters have massed in Tahrir Square in the Egyptian capital, Cairo, to demonstrate against continuing military rule.

Supporters of a variety of political groups, including Islamist, liberal and leftist forces, entered the square - a regular focal point for rallies.

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.

Analysis

Jon Leyne BBC News, Cairo

This is probably the biggest demonstration here since last November, but what is even more significant is the range of opposition forces gathered.

They are united by a range of issues, but particularly the disqualification of a number of presidential candidates.

They are trying to put maximum pressure on the military to ensure a free and fair election next month, and also that the handover of power to civilian rule goes ahead as planned at the end of June.

The gathering is yet another warning to the ruling Supreme Council of the Armed Forces (Scaf) that if there is not seen to be a proper transition to democracy then Egypt could be in for a second revolution.

The well-organised demonstration is peaceful, but takes Egypt into a new, tense phase that could last for several months. (© BBC MMXII 04/20/12)