Several protesters have died in central Cairo, as the latest rallies held by supporters of ousted Egyptian President Mohammed Morsi turn violent.
The BBC's Jeremy Bowen has seen seven dead bodies and many people badly injured near central Ramses Square.
The protests are taking place two days after Muslim Brotherhood camps were broken up, leaving at least 638 dead.
Protests are also being held outside Cairo. Four people were reportedly killed in clashes in Ismailia.
In the wake of Wednesday's violence, police have been authorised to use live ammunition in self-defence.
With a state of emergency still in force, BBC journalists described the atmosphere as tense.
Hundreds of people gathered at a nearby mosque after the Muslim Brotherhood, which backs Mr Morsi, appealed to its supporters to demonstrate after Friday prayers in a "march of anger".
The demonstrations are taking place under the slogan "the people want to topple the coup" - referring to the military's removal of Mr Morsi on 3 July.
His supporters have been urged to converge on Ramses Square from a number of mosques throughout the city.
Security in the capital is tight, with many armoured personnel carriers on the streets.
Entrances to Tahrir Square, the focus of demonstrations that led to the toppling of President Hosni Mubarak in 2011, were also reported to have been blocked off by the army.
State TV said the military was deploying to protect "important and vital facilities".
Members of groups opposed to Mr Morsi - the National Salvation Front and Tamarod - are reported to have called for counter-demonstrations in response to the Muslim Brotherhood protests.
There have also been calls for people to protect their neighbourhoods and churches throughout the country.
Egypt's Coptic Christian community has been targeted by some Islamists who accuse the Church of backing the army's overthrow of Mr Morsi last month.
The Egyptian Initiative for Personal Rights, an NGO, says 25 churches, along with private homes and businesses belonging to Copts and other Christian denominations, were attacked on Wednesday and Thursday.
There are fears of renewed bloodshed after authorities said the police were entitled to use live ammunition to protect themselves and key state institutions from attack.
Reports say there were renewed attacks on security forces on Thursday, with at least seven soldiers and a policeman killed in the Sinai peninsula and another police officer killed in the central city of Assiut.
US Republican Senator John McCain told BBC Newsnight that the ousting of President Morsi was a "coup" and President Obama should have cut off aid to Egypt as a result.
The US has been careful not to use the word coup as under US law this would mean stopping aid.
"I am confused that we would not enforce our own laws," he said.
"That sends a message of tolerance of brutality, of ineffective American leadership to the Muslim world, that the United States of America at least condones this kind of behaviour, which we cannot."
'Maximum restraint'
Meanwhile, Egypt's interim leaders have criticised remarks by President Barack Obama on Thursday.
On Thursday, Mr Obama condemned the government's actions in ordering security forces to break up the protest camps, and cancelled joint military exercises.
He said co-operation could not continue while civilians were being killed. However, he stopped short of cutting $1.3bn (£830m) in aid that the US gives to Egypt.
The Egyptian presidency said in a statement in the early hours of Friday that Mr Obama's words were "not based on fact" and would "embolden armed groups".
It said Egypt was facing "terrorist acts".
Wednesday's bloodshed has drawn widespread international condemnation.
Late on Thursday, the UN Security Council met in emergency session at the request of France, Britain and Australia.
Following the meeting, Argentina's ambassador to the UN, Maria Cristina Perceval, said the Council called for the Egyptian government and the Muslim Brotherhood to exercise "maximum restraint" and to end the violence.
Turkey, which described Wednesday's events as a "massacre", has recalled its ambassador to Cairo "to discuss the latest developments".
On Friday, the German government warned that further clashes "could plunge Egypt into a chaos of violence and counter-violence and further escalation".
It called for dialogue between the opposing parties, and also widened a travel alert for German citizens, advising them to stay away from the whole of Egypt.
Wednesday's violence began when armoured bulldozers moved into the two Cairo protest camps.
The smaller of the two camps, at Nahda Square, was cleared quickly but clashes raged for several hours in and around the main encampment near the Rabaa al-Adawiya mosque. The mosque was badly damaged by fire.
Egyptian interim Prime Minister Hazem Beblawi said the authorities had to restore security.
Mr Morsi, Egypt's first democratically elected president, is in custody accused of murder over a 2011 jailbreak. His period of detention was extended by 30 days on Thursday, state media said.
Are you in Cairo? Please send us your comments and eyewitness accounts using the form below.
Send your pictures and videos to yourpics@bbc.co.uk or text them to61124 (UK) or +44 7624 800 100 (International). If you have a large file you can upload here.
