Dozens of Mohamed Morsi's supporters were shot dead early Saturday in the deadliest incident in a month as violence erupted after huge rallies for and against the ousted Islamist president.
Morsi's camp said more than 100 people were killed. An AFP correspondent counted 37 bodies in an Islamist-run field hospital at Cairo's Rabaa al-Adawiya mosque, and the emergency services said other hospitals received 29 corpses.
In the wake of the bloodshed, Egypt's interior ministry insisted security forces had not used live fire, and blamed the clashes on Islamists.
Interior minister Mohammed Ibrahim also warned that pro-Morsi demonstrations would be dispersed "soon."
The latest violence erupted at dawn outside the mosque, where Morsi loyalists have been camped since the week before the military ousted him on July 3, with police firing tear gas at stone-throwing protesters on the airport road, said the official MENA news agency.
Birdshot and live rounds were fired, but it was unclear from which side. Witnesses told AFP that the police used live bullets, which the interior ministry denied.
By midday on Saturday, medical workers began ferrying bodies wrapped in white shrouds to hospitals, carrying them on blood-soaked stretchers past a furious throng of Morsi loyalists.
"Allahu akbar! (God is greatest)," chanted the crowd that formed a corridor to waiting ambulances.
Some wept and women ululated defiantly as each body was taken from the makeshift morgue in a marble-floored section of the mosque.
Medics at the field hospital said a total of 75 people were killed.
Mohamed Sultan of the health ministry's emergency services gave a toll of 29 dead, excluding the 37 at the Rabaa al-Adawiya field hospital. The ministry said 177 people were wounded.
The Islamist Anti-Coup Coalition that organises the Rabaa al-Adawiya protest said "over 100 people" were killed.
It was the deadliest incident since 53 people were killed outside the Republican Guard headquarters in the capital on July 8.
Thousands of supporters and opponents of the coup also took to the streets of second city Alexandria on Friday, sparking fierce clashes that killed at least eight and wounded 194.
The latest violence was roundly condemned by Britain and the European Union.
British Foreign Secretary William Hague urged "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".
The EU urged "a rapid move to an inclusive transformation process" that would include the Muslim Brotherhood.
Egypt's interior ministry defended the actions of security forces, with spokesman General Hany Abdel Latif saying police "did not use more than tear gas".
He accused Islamists of firing on the security forces, wounding 14 policemen, including two who were in critical condition after being shot in the head.
Interior minister Mohamed Ibrahim said security forces would act to disperse the pro-Morsi demonstrations "in a legal fashion" and "as soon as possible".
He said that security forces would seek to ensure "the minimum losses possible" and expressed the hope that Morsi loyalists would "comes to their senses" and go home.
The bloodshed came hours after army chief General Abdel Fattah al-Sisi called for a mass show of support for a crackdown on "terrorism".
Hundreds of thousands of anti-Morsi protesters obliged, thronging Cairo's Tahrir Square and around the Ittihadiya presidential palace.
A spokesman for army-installed president Adly Mansour said the numbers "affirmed the rejection of terrorism", MENA said.
But the Anti-Coup Coalition said its own turnout on Friday showed many "reject the bloody, military fascist coup that wants to set the wheel of history back".
On Friday, authorities remanded Morsi in custody for 15 days, accusing him of the "premeditated murder of some prisoners, officers and soldiers" when he broke out of prison during the 2011 uprising that toppled veteran strongman Hosni Mubarak, MENA said.
He also stands accused of conspiring to "storm prisons and destroy them... allowing prisoners to escape, including himself".
The military has so far kept Morsi's whereabouts secret to avoid attracting protests by his supporters.
Egypt, the Arab world's most populous country, has been rocked by violence that has now killed some 300 people since the coup.
Political polarisation has raised fears of prolonged violence, and even a militant backlash.
The military is already facing daily militant attacks in the Sinai Peninsula bordering Israel.
Analyst Mustafa Kamel el-Sayyad told AFP that Sisi had become "the strong man of the new regime", adding that "much of the population" supports his actions against the Brotherhood.
"On everything related to security, he has decisive influence," he said.
