An Egyptian man walks between lines of bodies wrapped in shrouds at a makeshift morgue in Cairo on Thursday, following a crackdown on the protest camps of supporters of ousted president Mohamed Morsi the previous day. Photo: AFP

Egypt's Muslim Brotherhood Thursday called on followers to march in protest in Cairo and warned that anger is "beyond control," after hundreds of people were killed in a security crackdown on the Islamist movement, leading to fears of more violence in the populous Arab state.

The crackdown has drawn condemnation from around the world, and also led Washington to cancel joint military exercises with Egypt next month.

A health ministry official said on Thursday that 525 people were killed and more than 3,500 injured in fighting around the country.

However, Gehad el-Haddad, a spokesman for the Brotherhood, Thursday said the death toll was eight or nine times bigger than the official toll.

According to Haddad, the movement and its allies suffered a strong blow from the security crackdown, and their central coordination has been lost.

"After the blows and arrests and killings that we are facing, emotions are too high to be guided by anyone," he told Reuters.

The Brotherhood called for marches in the capital to protest the deaths.

In Cairo, hundreds of supporters of the Brotherhood stormed a government building and set a fire at its entrance.

In Alexandria, Egypt's second biggest city, protesters were on the move by early afternoon.

State television quoted the interior ministry as saying that Egyptian security forces will use live ammunition to counter any attacks against themselves or public buildings.

A government statement said Thursday it is determined to confront "terrorist acts" by the Brotherhood, but it also sought an "inclusive political process" open to anyone who was not involved in violence.

Funerals of those killed will be held throughout the day, and on Friday, the main Muslim day of prayer, anger could spill onto the streets.

"I think tomorrow will be a big day for protests throughout Egypt, with the potential for violence being very high," Reuters quoted Yasser el-Shimy, an Egypt analyst with the International Crisis Group, as saying.

Egypt's Interim Prime Minister Hazem al-Beblawi late Wednesday defended security forces' operations, saying they showed "self-restraint."

Beblawi said that the government remained committed to an army-drafted roadmap calling for elections in 2014.

The military, led by Abdel Fattah al-Sisi, will continue pushing forward elections in Egypt because Sisi is under a lot of pressure due to international condemnation and has committed to holding elections according to the military's roadmap, He Wenping, a research fellow with the Institute of West Asian and African Studies at the Chinese Academy of Social Sciences, told the Global Times, adding that the military's legitimacy would falter if it didn't push forward a democratic election.

On Thursday, US President Barack Obama condemned the crackdown and said the US had canceled joint military exercises scheduled for next month.

"The United States strongly condemns the steps that have been taken by Egypt's interim government and security forces," Obama said from his vacation home on the Massachusetts island of Martha's Vineyard. "We deplore violence against civilians. We support universal rights essential to human dignity, including the right to peaceful protest."

He also noted that Washington is not backing either side in the standoff.

Ahmed Yehya, a research fellow with Cairo-based Al-ahram Center for Political and Strategic Studies, told the Global Times that Egyptians have shown discontent over the US' repeated interference in affairs in the Middle East, and a "US intervention at this time will definitely trigger more backlash."

China's foreign ministry Thursday said China is "deeply worried by recent developments" in Egypt. "China calls upon all parties to treat the interests of the Egyptian state and citizens with maximum concern, to exercise maximum restraint and to avoid more casualties," said the ministry.

Turkish Prime Minister Recep Tayyip Erdogan Thursday called for an urgent UN Security Council meeting over the crackdown and described the killings as a "very serious massacre."

In Europe, Paris, London, Berlin and Rome summoned Egypt's ambassadors to voice their strong concern.

Italian Foreign Minister Emma Bonino said on Thursday that EU foreign ministers are likely to meet next week to discuss Egypt, Reuters reported.

Meanwhile, UN rights chief Navi Pillay demanded an "independent, impartial, effective and credible investigation of the conduct of the Egyptian security forces."

However, the United Arab Emirates and Bahrain separately voiced support for the Egyptian government's crackdown.

Agencies contributed to this story