6 December 2012 Last updated at 23:37 ET
The Republican Guard has clashed with protesters outside the presidential palace in Cairo
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Egypt was braced for a day of fresh protests as opposition leaders considered a call for dialogue by President Mohammed Morsi.
Mr Morsi, under fire for his recent expansion of powers to rule by decree, has invited all major political factions to a meeting on Saturday.
His call came hours after clashes in Cairo left five dead and hundreds hurt.
Late on Thursday the Muslim Brotherhood, which backs Mr Morsi, said its Cairo offices had been set on fire.
Police also fired tear gas to disperse hundreds of protesters gathered outside the president's house in his hometown of Zagazig, north of Cairo.
CrisisUS President Barack Obama called Mr Morsi on Thursday to express his "deep concern" over the recent violent protests, the White House said.
He welcomed Mr Morsi's call for talks, but stressed they should be "without preconditions", a statement said.
Egypt has been plunged into crisis since President Morsi issued a decree on 22 November stripping the judiciary of any power to challenge his decisions.
However, he says the decree would be cancelled after a referendum on a new constitution planned for 15 December, whatever the result.
Nobel prize winner Mohamed ElBaradei, who is chief co-ordinator of the opposition National Salvation Front movement, expressed dismay at Mr Morsi's speech.
"We had hoped that the president would answer the continuing calls to rescind the constitutional decree and delay the referendum until there's national consensus on the constitution," he said in a televised address.
"We had wanted the president to have a comprehensive dialogue to save the country from the split that threatens it."
The National Salvation Front said it was assessing the offer of talks.
President Morsi said supporters of the Mubarak regime were behind recent violence
But another leading activist group, the April 6 movement, appeared to reject the offer, Reuters reported.
The group - which played a major role in last year's revolt against Hosni Mubarak - said on its Facebook page that protests on Friday would deliver a "red card" to Mr Morsi.
Other opposition groups also called for protests after Friday prayers at mosques and in squares across Egypt, Reuters said.
On Wednesday night and Thursday morning thousands of supporters and opponents of President Morsi fought outside the presidential palace using rocks, petrol bombs and guns.
Egypt's elite Republican Guard restored order and told rival demonstrators to leave by mid-afternoon.
President Morsi's supporters withdrew but opposition protesters remained, penned back by a barbed wire barricade guarded by tanks.
By nightfall their numbers had swelled to several thousand.
Mr Morsi has confirmed that the referendum on a new constitution would go ahead as planned, saying that if the constitution was voted down, another constituent assembly would be formed to write a new draft.
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.
Continue reading the main story
- Divisions likely to deepen
- Q&A: President v judiciary
- Old and draft charters compared
- Who holds the power?
Egypt was braced for a day of fresh protests as opposition leaders considered a call for dialogue by President Mohammed Morsi.
Mr Morsi, under fire for his recent expansion of powers to rule by decree, has invited all major political factions to a meeting on Saturday.
His call came hours after clashes in Cairo left five dead and hundreds hurt.
Late on Thursday the Muslim Brotherhood, which backs Mr Morsi, said its Cairo offices had been set on fire.
Police also fired tear gas to disperse hundreds of protesters gathered outside the president's house in his hometown of Zagazig, north of Cairo.
CrisisUS President Barack Obama called Mr Morsi on Thursday to express his "deep concern" over the recent violent protests, the White House said.
He welcomed Mr Morsi's call for talks, but stressed they should be "without preconditions", a statement said.
Egypt has been plunged into crisis since President Morsi issued a decree on 22 November stripping the judiciary of any power to challenge his decisions.
However, he says the decree would be cancelled after a referendum on a new constitution planned for 15 December, whatever the result.
Nobel prize winner Mohamed ElBaradei, who is chief co-ordinator of the opposition National Salvation Front movement, expressed dismay at Mr Morsi's speech.
"We had hoped that the president would answer the continuing calls to rescind the constitutional decree and delay the referendum until there's national consensus on the constitution," he said in a televised address.
"We had wanted the president to have a comprehensive dialogue to save the country from the split that threatens it."
The National Salvation Front said it was assessing the offer of talks.
But another leading activist group, the April 6 movement, appeared to reject the offer, Reuters reported.
The group - which played a major role in last year's revolt against Hosni Mubarak - said on its Facebook page that protests on Friday would deliver a "red card" to Mr Morsi.
Other opposition groups also called for protests after Friday prayers at mosques and in squares across Egypt, Reuters said.
On Wednesday night and Thursday morning thousands of supporters and opponents of President Morsi fought outside the presidential palace using rocks, petrol bombs and guns.
Egypt's elite Republican Guard restored order and told rival demonstrators to leave by mid-afternoon.
President Morsi's supporters withdrew but opposition protesters remained, penned back by a barbed wire barricade guarded by tanks.
By nightfall their numbers had swelled to several thousand.
Mr Morsi has confirmed that the referendum on a new constitution would go ahead as planned, saying that if the constitution was voted down, another constituent assembly would be formed to write a new draft.
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.