CAIRO (AFP) - Egypt's Islamists have called for a "Friday of anger" after nearly 600 people were killed in a crackdown on their protest camps, as the United Nations urged "maximum restraint" from all sides.
The call raised fears of fresh violence and tested the commitment of supporters of ousted president Mohamed Mursi, after officials said 578 people were killed in Wednesday clashes, Egypt's bloodiest day in decades.
Renewed attacks on security forces were staged during a tense day on Thursday, with at least seven soldiers and a policeman killed in the Sinai Peninsula and another police officer killed in the central city of Assiut.
With the country under a state of emergency and many provinces hit by night-time curfews, the interior ministry ordered police to use live fire if government buildings came under attack.
International criticism of the violence poured in and the United Nations Security Council held an emergency meeting on the crisis.
Mr Gehad al-Haddad, a Brotherhood spokesman, announced Friday's marches on his Twitter account.
"Anti-coup rallies ... will depart from all mosques of Cairo and head towards Ramsis Square after (traditional Friday) prayer in 'Friday of Anger,'" he wrote.
Ms Laila Moussa, a spokesman for the Anti-Coup Alliance of Islamist groups opposing Mr Mursi's ouster, said similar protests were planned across the country.
She said Mursi loyalists, including at least two former members of parliament, had been arrested in dawn raids ahead of the protests.
On Thursday, Tamarod, the protest group that organised opposition to Mr Mursi's rule, also urged Egyptians to take to the streets.
It said they should turn out on Friday "to reject domestic terrorism and foreign interference."
Ahead of the marches, the army deployed along key roads in Cairo, blocking some with armoured personnel carriers.
The international community meanwhile expressed grave concern.
In New York, the Argentine ambassador to the UN, Ms Maria Cristina Perceval, whose country currently presides over the Security Council, said member states regretted the loss of life in Cairo.
She called for an end to the violence and spoke of the need to advance "national reconciliation," while the Council itself refrained from issuing a resolution or statement.
US President Barack Obama responded by announcing the cancellation of a joint US-Egyptian military exercise.
"While we want to sustain our relationship with Egypt, our traditional cooperation cannot continue as usual when civilians are being killed in the streets and rights are being rolled back," he said.
But despite scrapping the Bright Star exercise, which has been scheduled every two years since 1981, he stopped short of suspending Washington's annual US$1.3 billion (S$1.65 billion) in aid to Egypt.
And the US State Department warned citizens not to travel to Egypt and called on those already there to leave.
Egypt's presidency responded defiantly to Mr Obama's remarks, warning that "statements not based on facts may encourage violent armed groups."
"The presidency appreciates US concern for developments in Egypt, but it wished it could have clarified matters," said the statement on the official MENA news agency.
Governments in several European capitals summoned Egyptian envoys to voice their concern.
Mursi-supporter Ankara recalled its ambassador to Cairo in protest, prompting Egypt to take the same measure with its envoy to Turkey.
UN rights chief Navi Pillay meanwhile called for "an independent, impartial, effective and credible investigation of the conduct of the security forces."
The toll suggested "an excessive, even extreme use of force against demonstrators," she said.