Updated

Backers of Egypt's ousted president Mohamed Morsi pledged to stage daily demonstrations, as security forces besieged a Cairo mosque full of Islamist protesters after a day of clashes on Friday that left more than 80 dead.

The fresh call for protest marches raised fears of more violence in Egypt, with the country already reeling from the deaths of at least 578 people on Wednesday when police cleared camps set up by loyalists of the deposed Islamist leader.

That crackdown continued to draw strong condemnation from the international community on Friday with EU foreign affairs chief Catherine Ashton calling for the bloc to adopt "appropriate measures" in response.

The siege of the Al-Fath mosque in the Ramsis area came at the end of what Islamists billed a "Friday of anger" marked by clashes between security forces and Morsi supporters, who have vowed to fight for his reinstatement after the military ousted him on July 3.

Security officials quoted by the official MENA news agency said "armed elements" were "shooting security forces and police from inside the mosque."

Morsi's Freedom and Justice Party (FJP) said in a statement there were "thousands of people trapped" in the mosque.

The FJP appealed for the prevention of another "massacre" after more than 200 people were killed at Rabaa al-Adawiya mosque on Wednesday, sparking nationwide clashes.

It was not possible to independently verify the numbers in the mosque.

A demonstrator inside the mosque said soldiers offered to evacuate the women but insisted on questioning the men, which the protesters refused.

The protester inside the mosque who spoke to AFP said there were almost 1,000 people holed up in the house of worship.

"The gunfire has ended," she said. "Thugs tried to storm the mosque but the men barricaded the doors."

It was not clear whom she meant by "thugs."

Friday's unrest started as Morsi supporters emerged from mosques in the capital to protest and violence erupted almost immediately, with gunshots ringing out in Cairo and security forces firing tear gas.

In the capital, a man leapt off a bridge near a police station to escape shooting as police armoured vehicles advanced on protesters, witnesses said.

An AFP correspondent counted at least 19 bodies in one Cairo mosque, while witnesses said more than 20 corpses had been laid out in a second mosque.

Elsewhere in Egypt, 10 people were killed by security forces and dozens injured in the canal city of Suez when they gathered to protest in defiance of the curfew.

Their deaths brought to 83 the number killed in nationwide violence although the Muslim Brotherhood's political arm, the Freedom and Justice party, spoke of 130 killed in Cairo alone.

Marches were also reported in the Mediterranean city of Alexandria, in Beni Sueif and Fayyum, south of Cairo, and in the Red Sea resort town of Hurghada.

The demonstrations ended shortly after a night-time curfew came into effect but Anti-Coup Alliance spokesman Gehad El-Haddad told AFP that Morsi loyalists would hold "daily anti-coup rallies" going forward.

The Egyptian cabinet issued a defiant statement after the unrest, saying it was confronting a "terrorist plot."

"The cabinet affirms that the government, the armed forces, the police and the great people of Egypt are united in confronting the malicious terrorist plot by the Muslim Brotherhood," it said.

And the interior ministry, which authorised police to use live fire if government buildings came under attack, accused the Brotherhood of attacking police stations, saying it foiled attempts to storm buildings.

Meanwhile, in Jordan, Morocco and the Palestinian territories, hundreds joined demonstrations in support of the Brotherhood.Wednesday's crackdown on the protest camps has polarised Egypt, splintering the army-installed government and drawing forceful international condemnation.

The United Nations said it would dispatch Jeffrey Feltman, under secretary general for political affairs, to Cairo next week.

But Egypt continued to defend the crackdown and announced it was cancelling naval exercises with Turkey to protest Ankara's condemnation.

Turkey, which backs Morsi, has recalled its ambassador to Cairo over the violence, prompting a tit-for-tat move by Egypt.

The EU's foreign policy chief said the violence was "shocking".

"I have asked member state representatives to debate and coordinate appropriate measures to be taken by the European Union in response to the situation in Egypt," said Ashton.

French President Francois Hollande on Friday discussed the crisis with counterparts in London, Berlin and Rome.

Germany said it would review ties with Cairo, and joined France and Britain in calling for EU talks on the situation, which are expected to take place on Monday.

On Thursday, the UN Security Council held an emergency meeting on Egypt, calling for an end to the violence and "national reconciliation".

President Barack Obama said the US was cancelling a joint US-Egyptian military exercise, but he stopped short of suspending Washington's annual $1.3 billion in aid.

However, the international response was not uniformly critical, with Saudi Arabia and Jordan saying they backed Egypt's fight against "terrorism".

King Abdullah said Saudi Arabia stood "with its Egyptian brothers against terrorism, deviance and sedition, and against those who try to interfere in Egypt's internal affairs".

The unrest pushed up oil prices on fears it could impact Suez Canal traffic or spark further Middle East unrest, analysts said.