Thirty-six Islamist prisoners were killed during an attempted jailbreak in Egypt, police say, bringing to almost 800 the death toll in five days as authorities continued a crackdown on supporters of ousted president Mohamed Morsi.
The bloodshed in Egypt has drawn widespread international condemnation, with senior European Union diplomats set to hold emergency talks on Monday to discuss the situation and future EU action.
There were conflicting reports of how the deaths occurred but the Egyptian interior ministry said the prisoners had taken an officer hostage and died after suffocating on tear gas.
"Thirty-six of the prisoners died of suffocation and crowding after tear gas was used to stop their escape," the ministry said.
The killings were the latest in five days of bloodshed sparked by a police and military operation to clear Islamists from protest camps in Cairo.
In his first remarks since the campaign was launched, military chief Abdel Fattah al-Sisi, who overthrew Morsi on July 3, warned security forces would confront any further violence from protesters.
"We will never be silent in the face of the destruction of the country," Sisi told top military and police commanders.
"We are very prepared for this," he said, pledging a "forceful" response to further attacks on police stations and government buildings.
The army and police have sent reinforcements to the Abu Zaabal prison, the scene of Sunday's deadly jailbreak attempt, the official MENA news agency reported.
The Muslim Brotherhood, Morsi's once banned movement that backed his election victory in 2012, said 35 prisoners were killed, revising an earlier toll of 52.
"The murder of 35 detained anti-coup protesters affirms the intentional violence aimed at opponents of the coup, and the cold-blooded killing of which they are targets," it said in a statement in English.
The Islamists said they cancelled "several marches" on Sunday, citing fears of vigilantes and snipers, but that others would go ahead.
At a mosque in the Dokki neighbourhood of Cairo, where one march was scheduled to begin, residents stood guard.
"We are waiting for them. I swear we will kill them if they approach the mosque," one said.
In the evening, the interior ministry announced a ban on vigilantes who have formed self-styled "popular committees" and urged citizens to respect a nightly curfew.
Elsewhere in Egypt, hundreds of protesters briefly marched in the Suez canal city of Ismailiya, an AFP correspondent said.
Two policemen were later killed in a shooting attack near the city, the interior ministry said.
