Egypt's Tamaroud youth movement has called on its supporters to take to the streets on Friday, while backers of deposed President Mohamed Morsi vowed to keep up their campaign to get the former leader reinstated.
Tamaroud said on Thursday night it wanted its sympathisers to form neighbourhood watch groups in order to stand up to Morsi's Muslim Brotherhood.
The youth group, which spearheaded protests paving the way for the overthrow of Morsi, urged Egyptians to "massively take to the streets forming neighbourhood watch groups in every road and alley, safeguarding our households, mosques and churches".
The call came a day after hundreds of people were killed when security forces cleared two pro-Morsi protest camps, ending sit-ins that began after the army toppled Morsi on July 3.
Morsi supporters took to the streets in several governorates on Thursday night, including in Fayom, Minia and Asiut.
Earlier in the day, the Interior Ministry authorised police to use deadly force to protect themselves and key state institutions from attacks, after state media said hundreds of Morsi supporters attacked the local government offices in Giza and set them ablaze.
"The Interior Ministry has instructed all forces to use live ammunition to counter any attacks on government buildings or forces," the ministry said in a statement.
Protesters have attacked police stations and other official buildings across the country over the past two days.
Death toll disputed
The Health Ministry said that 525 people were killed in the clearings and subsequent clashes across the country on Wednesday, and more than 3,500 injured.
Officials from the Muslim Brotherhood have said the true death toll was far higher, with a spokesman saying 2,000 people had been killed in the "massacre."
"After the blows and arrests and killings that we are facing, emotions are too high to be guided by anyone," said Gehad el-Haddad, a spokesman for the Muslim Brotherhood, adding that anger within the movement was "beyond control".
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Hundreds of bodies were packed into a Cairo mosque which had been pressed into service as a makeshift morgue.
Witnesses said most of the dead were killed by gunfire, many of them shot in the dead. Volunteers poured cold water and ice over the bodies to keep them from rotting in the harsh summer heat.
Families had hoped to bury their dead on Thursday, but several of them said they were unable to acquire the proper permits. The Health Ministry wanted them to accept death certificates that said their relatives committed suicide, they said.
The army-backed interim government has defended the crackdown, saying authorities had no choice but to act.
Authorities imposed an evening curfew on Wednesday, and also declared a state of emergency, which will last for one month. The latter gives security forces the power to detain people indefinitely.