BBC Arab Affairs Analyst
Cadets were taking revenge of the alleged abuse of a colleague
Egyptian army cadets in plain clothes have been filmed pelting a police station with stones in a town south of the capital Cairo.
Mobile phone footage was posted by Misrdigital, a blog campaigning against police brutality and corruption.
One sequence showed the cadets trying to overturn a car, said to belong to the chief district police officer.
They were reportedly taking revenge for the alleged abuse by the police of one of their colleagues.
Newspaper editors have told the BBC they received clear orders from the army not to publish any details of the incident, which happened on Sunday evening.
The army remains an off-limit topic for an otherwise vociferous independent media in Egypt. Those who violate the taboo can risk imprisonment.
State of disintegration
There is a history of tension between police officers and the army, that have occasionally degenerated into violence.
One commentator, who wanted to remain anonymous, said the incident showed the extent of chaos in Egypt, where even army cadets who are supposed to show restraint and discipline can behave like a mob.
It also showed that extent of resentment all Egyptians, including members of the armed forces, feel toward the police in Egypt, he added.
The executive editor of the independent al-Doustoor daily, Ibrahim Mansoor, told the BBC his newspaper was banned from publishing the story.
Mr Mansour said the incident "was part of the state of disintegration in Egypt. There are intense power struggles between institutions, with each one trying to demonstrate that it is the strongest".
Not a day goes by in Egypt without clashes or demonstrations, he added.