The Guardian reports: A video of a protester being beaten and stripped naked has galvanised protests against the police and government in Egypt.

Hamada Saber, a middle-aged man, remained in a police hospital on Saturday, the morning after he was shown on television, dragged over naked tarmac and beaten by half a dozen policemen who had pulled him to an armoured vehicle near the presidential palace.

President Mohamed Morsi’s office promised an investigation into the incident, which followed the deadliest wave of bloodshed of his seven-month rule. His opponents say it proves that he has chosen to order a brutal crackdown like that carried out by Hosni Mubarak against the uprising that toppled him in 2011.

Another protester was shot dead on Friday and more than 100 were injured, many seriously, after running battles between police and demonstrators who attacked the palace with petrol bombs.

That unrest followed eight days of violence that saw dozens of protesters killed in the Suez Canal city of Port Said and Morsi respond by declaring a curfew and state of emergency there and in two other cities.

“Stripping naked and dragging an Egyptian is a crime that shows the excessive violence of the security forces and the continuation of its repressive practices – a crime for which the president and his interior minister are responsible,” the liberal politician Amr Hamzawy said on Twitter.

The incident recalled the beating of a woman by riot police on Tahrir Square in December 2011. Images of her being dragged and stomped on – her black abaya cloak torn open to reveal her naked torso and blue bra – became a rallying symbol for the revolution and undermined the interim military rulers who held power between Mubarak’s fall and Morsi’s rise.