BBC:

"It appears that clashes began after some of the Morsi supporters tried to block a main road in the area, and security forces responded.

The state news agency Mena quotes a security official as saying they had been trying to stop fighting between rival sides, and that eight security personnel had been injured.

The official added that live fire had not been used, only tear gas.

But our correspondent says medics at the hospital believed about 70% of the casualties were caused by live fire - with many of the victims hit in the chest or head by snipers firing from rooftops.

Ahmed Nashar, a Brotherhood spokesman witnessed what happened near the Nasr City mosque where demonstrators built a wall to protect themselves.

"When I arrived, bullets were whizzing past my ears," he told the BBC. "Today was just brutal - people were fired at, with live firearms."

Our correspondent says Morsi supporters are furious about the role the military is taking, and in particular the head of the army, General Abdel Fattah al-Sisi, whom they say is killing Egyptians."

At the scene, Quentin Sommerville for the BBC reports from Cairo:

"There were pools of blood all over the field hospital. Many of the injured were in bad shape. Some had parts of their head missing - taken out by bullets.

The battle raged last night and all morning. We heard automatic gunfire. Protesters formed a human shield around us as shotguns and CS gas were fired towards us. There was the sound of outgoing shots too. The air was thick with tear gas and people were vomiting.

There was a child, maybe 12, covered in blood. He was deathly white. They closed the doors at the hospital as they could not accept more wounded, but the ambulances were still arriving.

As we left, a child was dragged from a car by the Morsi supporters outside the mosque. He was given a very serious beating."

Interior Minister Ibrahim said that ousted President Morsi would be transferred to Torah Prison, where ousted former President Mubarak is being held.