Egypt's main opposition bloc has backed calls for President Mohamed Morsi to step down, a day after deadly clashes left the government scrambling to contain the fallout from footage of police brutalising a man.

A statement from the National Salvation Front on Saturday signalled a harder line from the opposition coalition which has spearheaded protests against President Morsi since November.

"The Salvation Front completely sides with the people and its active forces' calls to topple the authoritarian regime and the Muslim Brotherhood's control," it said, urging Egyptians to stage peaceful protests.

It demanded Morsi's trial for crimes of "killings and torture" and ruled out dialogue with the presidency until "the bloodletting stops and those responsible for it are held accountable".

Police clashed with protesters outside Cairo's presidential palace on Friday night, leaving at least one person dead. Television footage, meanwhile, showed police beating and dragging a naked man into an armoured vehicle.

In all, more than 50 people were injured on Friday, including at least five policemen.

The beating was "an inhumane spectacle ... no less ugly than the killings of martyrs, which is considered a continuation of the security force's programme of excessive force", the NSF said.

Mohammed Ibrahim, the country's interior minister, has ordered an investigation to "hold accountable" the policemen who beat the man, his office said.

Prosecutors say the man, a 50-year-old construction painter sent to a police hospital, was found carrying petrol bombs.

The presidency said it was "pained by the shocking footage of some policemen treating a protester in a manner that does not accord with human dignity and human rights".

It would follow the interior ministry's investigation of what it called an "isolated act".

It said that the incident should not be used as justification for attacks on state institutions.

No fresh protests

There was no sign of any protests on Saturday, as debris-littered streets around the presidential palace reopened to traffic.

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The odour of tear gas lingered near the palace, its outer wall scrawled with graffiti including "Topple the regime" and "Freedom".

In central Cairo's iconic Tahrir Square, protesters threw stones and bottles at Prime Minister Hisham Qandil's motorcade on Saturday morning, local media reported.

The premier said in a statement that he was "confronted by youths and troublemakers" and had "preferred to avoid a confrontation between them and security personnel".

Qandil also said that the country's economy was suffering from the current climate of uncertainty and the threat of violent protests.

President Morsi had earlier said that his government would deal decisively with violent protests and would hold opposition groups "political accountable".

Morsi's Facebook page said the protesters had initiated Friday's violence by trying to break into the palace.

The opposition, which accuses Morsi of betraying the revolution that toppled Mubarak two years ago, has distanced itself from the violence and urged demonstrators to exercise "utmost restraint".

Source: Agencies