Troops and gangs of plainclothes police attacked a mass march in Egypt’s capital Cairo last Saturday.
Tens of thousands were kettled by military police as they tried to reach the city’s army headquarters.
They were then attacked from all sides by gangs using knives and swords, and throwing bricks and firebombs.
One participant described the scene as “a war zone”. Over 300 people were injured.
The protest was against the failure of Egypt’s military rulers to address the demands of the revolutionary movement.
Protesters were demanding the prosecution of members of the former regime responsible for the deaths of activists earlier this year.
The generals’ response was the clearest signal so far that defence of their own authority and privilege is more important than the aims of the mass movement.
In February protesters were attacked by gangs mobilised by then dictator Hosni Mubarak’s ministers and police chiefs.
Now it seems that the same thugs are operating under the protection of the army.
This marks a serious challenge to the revolutionary movement.
It comes as the Muslim Brotherhood prepares to back the generals against the activists of the streets, militant workers and the new independent unions.
The Brotherhood is Egypt’s largest political organisation.
After furious debates within the organisation, its leaders have called for a “Friday of Stability” this week, 29 July.
They intend to mobilise in support of the generals’ efforts to halt the momentum of the revolution.
Their call is a calculated provocation to those in their third week of occupation of Tahrir Square.
This is a dangerous phase of the revolution, during which its enemies hope to weaken or even derail the struggle for further change.