Egypt's main opposition group on Saturday sided with calls to oust the ruling Islamists after deadly clashes left the presidency scrambling to contain fallout from footage of police brutalising a man.
A statement from the National Salvation Front signalled a harder line from the opposition coalition which has spearheaded protests against President Mohamed 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" after an "impartial investigation" and ruled out dialogue with the presidency until "the bloodletting stops and those responsible for it are held accountable."
Clashes on Friday night between protesters and police outside the presidential palace left one dead, and police were filmed beating and dragging off another man, following clashes last week that killed nearly 60 people.
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," it said.
A 23-year-old was shot dead and 91 people were injured in Friday's clashes, a medic said, while the interior ministry reported 15 of its men wounded by birdshot.
Police said they made 20 arrests, and they were filmed on television beating and dragging a naked man to an armoured vehicle, outraging Morsi's critics who compared the incident to practices under deposed president Hosni Mubarak.
Interior Minister Mohammed Ibrahim has ordered a probe 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."
There was no sign of any protests on Saturday, as debris-littered streets around the presidential palace reopened to traffic.
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, the Egyptian Dream Live television 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."
But the presidency has said security forces would deal with violent protests with "utmost decisiveness" and that it would hold opposition groups found to have incited deadly clashes as "politically 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."
The NSF had joined rival Islamists on Thursday in condemning violence and supporting efforts for a national dialogue, but insisted on a unity government and amendment of the Islamist-drafted constitution that has polarised the nation.
People took to the streets in several cities on Friday in a show of opposition to Morsi and his Muslim Brotherhood after deadly unrest swept Egypt last week, the worst violence since Morsi was elected in June.
Port Said accounted for most of the almost 60 people killed. Violence erupted there after 21 local supporters of a football club were sentenced to death a week ago over the killings of 74 people in post-match violence.
The crisis has sapped Morsi's popularity and complicated negotiations for a crucial $4.8-billion IMF loan that could help bail out the teetering economy.