An emergency meeting of the United Nations Security Council has ended with the council urging all parties in Egypt to end the violence.
The council has also called on Egypt's current rulers and supporters of Mohammed Morsi to exercise restraint, after hundreds of people were killed when troops and police crushed protests seeking the return of the deposed president.
The assault by security forces on Wednesday centred on two camps which supporters of the Mr Morsi set up in Cairo last month.
The latest death toll from the Egyptian health ministry has increased to 638 but the Brotherhood still says the number is much higher.
The unscheduled United Nations meeting was requested by France, Britain and Australia and follows strong reactions from UN officials. Secretary General Ban Ki-moon has condemned the violence in the strongest terms while UN human rights chief Navi Pillay has demanded an independent investigation.
United States President Barack Obama has also condemned the crackdown in his first comments since the violence began.
Mr Obama says the United States supports universal rights essential to human dignity, including the right to peaceful protest.
He says normal U.S. co-operation cannot continue with Egypt while civilians are being killed and a joint military exercise scheduled for next month has been cancelled.
Mr Obama stopped short of suspending $US1.3 billion in annual military aid but warned that Egypt has entered a more dangerous path.
Live firing approved
The Egyptian Government says it has authorised the police to use live ammunition in self-defence and to protect key institutions and a curfew is now in force in Cairo.
However, that has not stopped the violence, with hundreds of Muslim Brotherhood supporters storming a government building in Giza, near Cairo, and setting it ablaze.
Many more protesters marched in Egypt's second biggest city of Alexandria.
Local television footage has shown two buildings burning in Cairo and firefighters evacuating employees.
One of the buildings housed the offices of the Giza local government.
The Muslim Brotherhood is calling for further protest rallies following Friday prayers in what they are calling a "day of anger".
The protesters are demanding the reinstatement of former President Mohamed Morsi, who was deposed by the army six weeks ago after mass demonstrations against his rule.
A Muslim Brotherhood spokesperson, Gehad El-Haddad, says anger within the movement, which has millions of supporters, is beyond control, Reuters reports.
New Zealanders warned away
The Ministry of Foreign Affairs continues to advise New Zealanders to avoid all travel around North Sinai in Egypt.
The ministry also advises against all tourist and non-essential travel in other parts of the country.
A spokesperson says New Zealanders in the country should avoid all protests and large public gatherings, exercise a high degree of security awareness in public places and adhere to any instructions issued by local authorities.
There are currently 220 New Zealanders registered as being in the country and the ministry strongly advises those who are not registered to do so via the website www.safetravel.govt.nz.