Dozens of men wielding knives and machetes and hurling bricks and petrol bombs confronted protesters at the headquarters of Egypt's state security, they said.

It appeared to be the first time armed men in plain clothes had deployed in force against reform activists in central Cairo since Mubarak was forced to step down and hand power to the military, which has charted a course to democratic elections.

The scenes evoked attacks on protesters in Tahrir Square by men claiming loyalty to Mubarak during the 18-day uprising that led to his downfall. Since then, activists have pressed demands for deeper reform, including a major shake-up of the police.

Egyptian soldiers, on the streets since the start of the uprising, fired into the air for several minutes to disperse the protesters.

Reuters