By Heba Saleh BBC News, Cairo

The Muslim Brotherhood is outlawed in Egypt

The Egyptian authorities have deployed thousands of riot police in central Cairo to prevent Muslim Brotherhood demonstrators reaching parliament.

Brotherhood sources say at least six of their members were arrested as they tried to reach the building.

On Saturday, the authorities had arrested about 50 members of the group in different provinces of the country.

The Muslim Brotherhood, although banned, is considered Egypt's largest and most organised opposition force.

Police in full riot gear blocked off whole streets in the city centre to prevent access to parliament.

But hundreds of demonstrators appear to have managed to hold small protests in locations outside the city centre.

Assertive stance

The Muslim Brotherhood had called for the demonstration in support of its demands for political reforms ahead of this year's presidential election.

It wants the government to lift the emergency law and to abolish all restrictions which prevent political activity.

Like other Egyptian political forces, the Muslim Brotherhood fears the government plans to impose conditions that would make it impossible for credible candidates to challenge President Hosni Mubarak.

He has recently introduced a constitutional amendment that would allow the country to hold contested presidential elections for the first time.

The Brotherhood usually avoids confrontations with the state and concentrates instead on expanding its influence in society.