The protest rally was due to take place after prayers at the Saida Aisha mosque, in a popular neighbourhood close to the ancient citadel, but a police officer at the scene said "the mosque was closed and there is nobody inside".

Water cannons and prison vans were visible in the square near the mosque, in an apparent show of force to deter any gathering.

Except for baton-wielding anti-riot police, the square was empty, in a sharp contrast with the crowded streets nearby.

Three opposition parties -- the liberal Wafd, the Arab Nasserist Party and the leftist Tagammo -- said Wednesday they had secured permission to demonstrate, claims denied by the interior ministry.

"If a demonstration is held, the interior ministry will arrest its organisers," the government said in a statement published in Friday's newspapers.

The Muslim Brotherhood, the largest opposition group, said Thursday it would only take part in authorised demonstrations.

Emergency laws, which have been in force almost continuously since 1967, ban public protests. However, they are tolerated on university campuses, in stadiums and in mosque compounds.

Around 100 demonstrators and policemen were slightly injured in clashes on the central Tahreer square on March 20, the first day of the war, and several hundreds were arrested.

SPACE.WIRE