Three prominent activists will appear in court on Sunday for allegedly taking part in a violent and unauthorised protest under a new assembly law that has sparked public outcry.

Security has been beefed up around the trail venue: a police building in a prison compound on the outskirts of Cairo, Al-Ahram Arabic news website said.

Blogger Ahmed Douma and leading activist Ahmed Maher were arrested after allegedly assaulting policemen at an illegal protest outside a Cairo court where Maher was handing himself in.

An arrest order had been issued against Maher – founder of the April 6 Youth Movement and a symbol of the 2011 uprising that toppled autocrat Hosni Mubarak – for organising a separate illegal protest in late November.

Maher and Douma are in detention pending trial but third activist Mohamed Adel, will be tried in absentia, according to judicial sources.

London-based Amnesty International has said, "The charges against them may arise solely from their opposition activism."

Dozens of protesters, including leading female activists, have been arrested since the contentious protest law was issued two weeks ago, sparking fears of a widening crackdown on dissent.

The law requires organisers to seek authorisation three days ahead of any planned demonstration. Protests can be banned if deemed a threat to national security.

Since the ouster of Islamist president Mohamed Morsi in July, authorities have launched a sustained crackdown on his Islamist supporters in which hundreds have been killed and thousands others arrested.

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