Graphic footage of a naked Egyptian man being dragged across a street and beaten by at least eight riot policemen during a protest in Cairo on Friday night has intensifed popular fury at President Mohamed Morsi and sparked calls from Egypt's opposition for "an end to this regime of tyranny".

The video shows Hamada Saber, reportedly a 50-year-old unemployed labourer, lying on the ground outside the presidential palace in north-east Cairo, with his trousers around his ankles, being beaten with batons and fists before being dragged into a police van.

The scene is reminiscent of the "woman in the blue bra" – a protester stripped and beaten by soldiers during protests against military rule in December 2011, whose plight became a lightning rod for opposition dissent.

"I don't know how to describe this. It's appalling," said Khaled Dawoud, a spokesman for the National Salvation Front, a disparate coalition of liberal, secular and leftist opposition groups. "The name of the president has changed but his policies haven't," Dawoud added, calling for "an end to this regime of tyranny" but stopping short of calling for Morsi's resignation.

After a week of civil unrest across the country, in which nearly 60 people died, protesters had gathered outside the presidential palace in Cairo to intensify calls for Morsi's downfall, sparking clashes during which petrol bombs were thrown over the palace walls.

Amid the fighting, private television footage, corroborated by witness accounts, clearly shows Saber being beaten by police. The interior minister has since apologised for the attack and offered to resign.

Yet in a bizarre twist, Saber later claimed in an interview from a police hospital that the police had in fact saved him from thieving protesters. Saber's account sparked fears that he had either been threatened into silence, or paid off.

"Everything points to him having been coerced into not pressing charges at the ministry and being co-operative," wrote commentator Issandr el-Amrani. "What kind of regime would both beat this man and then force him to stand up on TV and say these things?" said Dawoud.

Saber's words were also contradicted by some members of his own family. His daughter Randa – who says she was present at the scene of the attack – called a television chatshow to dispute Saber's version of events, saying he was "afraid to talk".

For the opposition, the video is a clear sign that police reform – a key demand of the 2011 revolution – remains a low priority for the Morsi government, which some believe has become as authoritarian as Hosni Mubarak's dictatorship.

No policeman has been jailed for a role in the deaths of the 800 protesters killed during the 2011 revolution, while in a televised speech last Sunday Morsi praised the police for their part in recent clashes in the Suez canal region that left over 40 dead, many of them passersby killed by police snipers.

A spokesman for the Muslim Brotherhood, Gehad al-Haddad, said this week that the president needed more time to reform the police. "If it took them 60 years to build a system that corrupt," he said, "imagine how long it will take to reform it."

But Heba Morayef, head of the Egypt branch of Human Rights Watch, said Morsi had showed little reforming intent so far. "It's not just that he hasn't delivered on any changes, it's that he hasn't publicly acknowledged that there is a serious problem of police abuse," said Morayef.

The video is not the only film to have shocked Egypt in recent days. On Saturday, a women's rights group – Operation Anti-Sexual Harassment – released footage of a woman being gang-raped in Tahrir Square to highlight the dangers facing women on protests, and throughout Egypt in general. At least 25 women have been sexually assaulted in the square since protests restarted there last week – while according to a 2008 report by an Egyptian women's rights group, 83% of Egyptian women are harassed on a daily basis.