A Brotherhood spokesman, Ahmed Aref, told reporters that 66 were killed in the Cairo violence and another 61 were "clinically dead". He did not further explain their condition, but his comments suggested the official toll could go higher.
In chaotic scenes, pools of blood stained the floor and bodies were lined up under white sheets in a makeshift hospital near the site of the battles in eastern Cairo as doctors struggled to cope with the flood of dozens of wounded.
The extent of the carnage underlined the willingness of police to unleash deadly firepower against any expansion of Islamist-led protests demanding the reinstatement of Morsi.
Interim Vice President Mohamed ElBaradei, a longtime pro-democracy campaigner who backed the military's ouster of Morsi, raised one of the few notes of criticism of the bloodshed in the new military-backed leadership.
"I highly condemn the excessive use of force and the fall of victims," he wrote in a tweet, though he did not directly place blame for the use of force.
The bloodshed also pointed to the Islamists' readiness to challenge the security forces as Morsi's supporters try to win over public support for their cause.
The fighting, which began before dawn and stretched out over several hours, was the deadliest bouts of violence since the military ousted Morsi on July 3 in the wake of massive protests demanding his removal.
Soon after Morsi's fall, more than 50 of his supporters were killed in a similar outbreak of violence outside a headquarters of the Republican Guard.
A leading figure of Morsi's Muslim Brotherhood, Mohammed el-Beltagy, blamed the violence on army chief Gen. Abdel-Fattah el-Sissi's call for rallies on Friday.
"This is the mandate el-Sissi took last night ' to commit massacres and bloodshed against peaceful protesters denouncing the military coup," el-Beltagy said in a statement on his Facebook page.
At the makeshift clinic set up at the Rabaah al-Adawiya encampment, men shouted "God is great", and women wailed as bodies were loaded into ambulances to be taken for examination at hospitals. Bodies of more than a dozen men lay on the blood-splattered floor with white sheets over them.
"They aimed at killing the people. They aimed the head and the neck," said Ahmed Abdullah, a doctor at the field clinic, as he wiped tears from his eyes.
The Interior Ministry, which oversees the police force, said in a statement that residents in the district began clashing with the pro-Morsi marchers when their protest blocked a major artery. The ministry said police who intervened were trying to break up the two sides by firing tear gas.
Morsi ouster aftermath
Britain condemns use of force against protesters
London: British Foreign Secretary William Hague Saturday condemned the use of force against protesters during deadly clashes in Cairo and accused Egyptian security forces of using live rounds. "I am deeply concerned by recent events in Egypt, and condemn the use of force against protesters which has led to loss of lives," Hague said in a statement released by the Foreign Office. "I call on the Egyptian authorities to respect the right of peaceful protest, to cease the use of violence against protestors, including live fire, and to hold to account those responsible," Hague said. PTI
Will not label overthrow as coup: US
Washington: The US has said it will not declare the ouster of Mohammed Morsi as a coup in its own national interest, allowing it to continue providing $1.5 billion in annual military and economic aid. "We believe continued provision of assistance to Egypt, consistent with our law, is important to our goal of advancing a responsible transition to democratic governance," State Department spokesperson Jen Psaki said Friday. PTI