PARIS (AFP) -- Egypt's military rulers Thursday faced international condemnation over the bloody crackdown on Muslim Brotherhood protesters, with France warning of the threat of "civil war" and Turkey demanding UN action.

More than 500 people were killed in Wednesday's assaults on two Cairo protest camps of supporters of ousted Islamist president Mohamed Morsi in the country's worst violence in decades.

The United States led global outcry against the "deplorable" violence, while Paris, London, Berlin and Rome summoned Egypt's ambassadors to voice their strong concern.

Turkey's Prime Minister Recep Tayyip Erdogan, a Morsi supporter, called for an urgent UN Security Council meeting over Egypt's "massacre" of the demonstrators.

China was characteristically muted, appealing for "maximum restraint" from all parties, while fellow Security Council permanent member Russia only urged tourists to avoid trips to Egypt.

Only two Gulf states that have cracked down on Islamist groups within their own borders, the United Arab Emirates and Bahrain, initially voiced support for the Cairo military leaders.

French President Francois Hollande said "everything must be done to avoid a civil war" in Egypt, while his government conveyed France's "great concern over the tragic events" to Egypt's envoy.

"France is committed to finding a political solution and calls for elections to be held as soon as possible, in line with the commitments made by Egypt's transitional authorities," said a statement.

Britain also condemned the violence, expressed its "deep concern" to Egypt's envoy and urged "the greatest restraint."

Germany, whose Foreign Minister Guido Westerwelle has called for an end to violence and resumed negotiations, told Egypt's envoy its position "in no uncertain terms," said a ministry spokeswoman.

Turkey's Erdogan said "this is a very serious massacre... against the

Egyptian people who were only protesting peacefully". He also criticized the "silence" of the global community in the face of the bloodshed.

The United States did not initially object to the overthrow of Morsi -- Egypt's first democratically elected and Islamist leader -- and has avoided using the term "coup," which under U.S. law would have halted some $1.3 billion in annual military aid to Cairo.

But U.S. Secretary of State John Kerry's comments, in which he called for elections, appeared to fully recant his previously expressed support for Egypt's military-backed government.

"Today's events are deplorable and they run counter to Egyptian aspirations for peace, inclusion and genuine democracy," he said.