Cairo offices torched as Egypt death toll mounts
Hundreds of Muslim Brotherhood supporters have set fire to a government building in Giza, near the Egyptian capital, Cairo.
The move comes a day after security forces broke up the Brotherhood's protest camps, leaving hundreds dead.
Brotherhood members had been protesting for weeks about the army's overthrow of President Mohammed Morsi in July.
The government says 525 died nationwide on Wednesday, but the final toll is likely to be significantly higher.
Scores of bodies have not been registered, because the official count only includes bodies which have passed through hospitals.
The BBC's Khaled Ezzelarab has reported seeing at least 140 bodies wrapped in shrouds at the Eman mosque, close to the main protest camp at Rabaa al-Adawiya Square. These will not have been counted in the official toll.
The Muslim Brotherhood insists that more than 2,000 people died. It says 300 bodies were taken to the Eman mosque, and other bodies were taken to sports halls.
Reports speak of disputes between bereaved relatives and officials entrusted with documenting the causes of death.
The Muslim Brotherhood, the main source of Mr Morsi's support, had called for marches on Thursday, both in Cairo and Egypt's second city, Alexandria, to protest against Wednesday's deaths.
After attempting to storm the building housing the local government in Giza - Cairo's twin city on the west bank of the Nile - the protesters were repelled by police, according to state television.
Local TV footage showed two buildings burning, and firefighters evacuating employees.
State-run Nile News TV also reported clashes between Muslim Brotherhood members and residents in a suburb of Alexandria.
Armoured bulldozers had moved into the two protest camps in Cairo shortly after dawn on Wednesday morning.
The smaller of the two protest camps, at Nahda Square, was cleared quickly but clashes raged for several hours in and around the main encampment at Rabaa al-Adawiya. The mosque of the same name was damaged by fire.
Mobs later carried out reprisal attacks on government buildings and police stations as well as churches belonging to the country's Coptic Christian minority.
In a televised address on Wednesday evening, Egyptian interim Prime Minister Hazem Beblawi defended the operation, saying the authorities had to restore security.
He declared a state of emergency, but said this would be lifted as soon as possible.
Many countries have condemned the Egyptian security forces' actions.
Navi Pillay, the UN High Commissioner for Human Rights, has demanded an independent, impartial inquiry into what happened on Wednesday.
"The number of people killed or injured, even according to the government's figures, point to an excessive, even extreme, use of force against demonstrators," Ms Pillay said in a statement.
Turkish Prime Minister Recep Tayyip Erdogan described the events as a "very serious massacre".
US President Barack Obama is due to give a statement on the issue soon.
Mr Morsi, Egypt's first democratically elected president, was ousted by the military on 3 July.
He is now in custody, charged with murder over a 2011 jailbreak. His period of detention was extended by 30 days on Thursday, state media said.