Pro-democracy protesters in Cairo have been attacked with swords and petrol bombs by a mob of plainclothed men, according to reports.
Dozens of men armed with knives and machetes came face to face with demonstrators at the headquarters of Egypt’s state security.
It is believed to be the first attack on protesters since former Egyptian president Hosni Mubarak was ousted last month.
One of the key demands of the protest movement was an upheaval of the security forces, who have a reputation for brutality.
The latest skirmishes were a stark reminder of the attacks on protesters in the capital’s Tahrir Square by men claiming loyalty to Mubarak during the 18-day uprising that led to his downfall.
Activists have since been pressing for deeper reforms, including a significant 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.
As they ran, witnesses said the protesters were confronted by 200 men they described as thugs.
The state news agency said the demonstrators were trying to break into the building.