Egyptian President Mohammed Morsi calls for dialogue
Egyptian President Mohammed Morsi has called for a meeting with the opposition on Saturday to defuse a political crisis.
He was speaking hours after five people died and 644 were injured in clashes between his opponents and supporters.
Mr Morsi said he supported the right to protest but alleged that some people had been paid to foment violence.
The Muslim Brotherhood - which backed Mr Morsi for the presidency - says its Cairo HQ has been set on fire.
In a televised speech, Mr Morsi expressed sorrow over the deaths in recent days.
He said that 80 people had been detained as they had been "implicated in violent acts".
He blamed supporters of the ousted regime of President Hosni Mubarak for being behind recent violence.
Mr Morsi offered little in the way of concessions to his opponents but said that a controversial article in a recent decree which gave him sweeping powers could be modified.
US President Barack Obama welcomed Mr Morsi's call for talks, but stressed they should be "without preconditions", the White House said in a statement on Thursday.
"President Obama called President Morsi today to express his deep concern about the deaths and injuries of protesters in Egypt," the statement said.
"The president emphasised that all political leaders in Egypt should make clear to their supporters that violence is unacceptable," it added.
Mr Morsi's recent decree stripped the judiciary of any power to challenge his decisions.
The decree would be cancelled after a referendum on a new constitution planned for 15 December, whatever the result, Mr Morsi added.
Mr Morsi confirmed that the referendum would go ahead as planned, saying that if the constitution was voted down, another constituent assembly would be formed to write a new draft.
The speech is likely to inflame an already heated situation in Egypt, the BBC's Jon Leyne reports from Cairo.
It is not clear whether the opposition will be willing to take up his offer of dialogue, given that none of their demands have been met, our correspondent adds.
There will be fears that the attacks on the Muslim Brotherhood's headquarters could be just the start of a new round of violence and confrontation, he says.
The April 6 movement, which played a prominent role in the 2011 uprising that ousted President Mubarak, has rejected Mr Morsi's offer of dialogue, Reuters reported.
The activist group has called for fresh protests on Friday against Mr Morsi, who narrowly won June's first free presidential election.
Earlier on Thursday, the army set up barricades outside the presidential palace after ordering protesters to leave the area.
Most anti-Morsi protesters had left the area around the palace by the 15:00 (13:00 GMT) deadline, though some opposition activists remained and their numbers increased as evening fell.
There is controversy over the proposed constitution.
Critics say the draft, drawn up by a body dominated by Morsi-supporting Islamists, was rushed through parliament without proper consultation and does not do enough to protect political and religious freedoms and the rights of women.
Four of Mr Morsi's advisers resigned on Wednesday - three others did so last week and the official Mena news agency reported a further resignation on Thursday.
The opposition said before Mr Morsi's speech that it will continue to hold demonstrations.
"We had many injuries last night, and we are not going to have their blood wasted," said an unnamed member of the National Salvation Front, a recently formed group which has united some of the most prominent anti-Morsi figures.
The National Salvation Front has brought together former presidential candidates such as leftist Hamdeen Sabahy, former Arab League head Amr Moussa, and Mohammed ElBaradei, the former head of the UN's nuclear watchdog.
The April 6 movement and other activist groups are mostly made up of young Egyptians who were opposed to President Mubarak's rule and many have turned against Mr Morsi in recent months.