Egypt's largest opposition group defied authorities and held anti-government protests in Cairo Sunday.

Several thousand riot police prevented the Muslim Brotherhood from holding a rally outside the Egyptian parliament as planned.

Instead, members of the group gathered in front of a Cairo mosque, shouting demands for political reforms. Authorities say they arrested at least 50 protesters.

Estimates of the crowd range from several hundred to 3,000. Smaller protests took place at two other Cairo locations.

Egyptian authorities had arrested another 50 Brotherhood members before the protests.

The Muslim Brotherhood calls for replacing Egypt's secular government with an Islamic state. The group was formally banned in 1954, but its members, running in elections as independents, hold enough seats to make the Brotherhood the largest opposition group in Egypt's parliament.