Sisi's challenge

Hundreds of thousands of Egyptians had poured onto the streets on Friday in response to a call by army chief General Abdel Fattah al-Sisi for nationwide demonstrations to give him backing to confront the weeks-long wave of violence.

His appeal was seen as a challenge to the Brotherhood, which organized its own rallies on Friday calling for the return of Morsi, who has been held in an undisclosed location since his ousting and faces a raft of charges, including murder.

Ibrahim said Morsi was likely to be transferred shortly to the same Cairo prison where former leader Mubarak is now held.

Leaders of the Brotherhood, a highly organized movement with grassroots support across Egypt, appealed for calm on Saturday, but activists at the vigil voiced fury.

Supporters of deposed Egyptian President Mohamed Morsi take part in a protest at the Rabaa Adawiya square, where they are camping, in Cairo, July 27, 2013. [Photo/Agencies]

"The people want the execution of Sisi," a cleric shouted to the crowd from a stage by the mosque. "The people want the execution of the butcher."

Interior Minister Ibrahim said the pro-Morsi sit-ins would "God willing, soon ... be dealt with" based on a decision by a public prosecutor, who is reviewing complaints from local residents unhappy with the huge encampment on their doorstep.

The European Union and major European powers deplored the violence. US Secretary of State John Kerry urged dialogue and restraint.

"At this critical juncture, it is essential that the security forces and the interim government respect the right of peaceful protest," he said. "This is a pivotal moment for Egypt."

The Pentagon said US Defence Secretary Chuck Hagel had spoken by phone with Egyptian army chief Sisi and urged steps "to prevent further bloodshed and loss of life."

Washington has delayed delivery of four F-16 fighters, part of the $1.5 billion in aid it provides every year, mainly in military hardware, but says it does not intend to cut off aid to a country seen as a vital ally and which has a peace deal with neighbouring Israel.

Turkey, a vocal supporter of Morsi, accused the West of turning a blind eye.

"Those who were silent when Egypt's national will was massacred are silent again when people are massacred," Prime Minister Tayyip Erdogan, who has faced down large protests against his own government this year, said in televised comments. "What happened to the EU (and) European values, where are those who go around giving lessons in democracy?"