At least 40 people have been killed in a shooting incident in Cairo, say officials and the Muslim Brotherhood, amid continuing unrest over the removal of President Mohammed Morsi.
The Brotherhood says its members were fired on while they were holding a sit-in at a Presidential Guard barrack.
But the army said a “terrorist group” had tried to storm the barracks.
Morsi, an Islamist and Egypt’s first freely elected president, was ousted by the army last week after mass protests.
Scores of people have been killed since the unrest began last weekend.
Morsi is believed to be held at the Presidential Guard Club, in the eastern Nasr City district of the capital.
There was a sombre mood in Cairo as people woke up to the news of killing and bloodshed.
Eyewitness accounts of what happened outside the Presidential Guards Club have inflamed the already simmering tensions. For Egyptians, it is shocking news no matter who started the gunfight.
The deadly incident is not the first. On Friday, three protesters were killed at the same spot in unclear circumstances but against a backdrop of a stand-off between the army and the pro-Morsi protesters.
The latest shooting is likely to lead to a political breakdown as the Islamist Nour party, the largest Salafist group, withdrew from marathon talks with interim president Adly Mansour to form a caretaker government.
His supporters – many of them members of the Muslim Brotherhood movement he comes from – have been staging a sit-in there demanding his reinstatement.
After Monday morning’s violence, the hardline Salafist Nour party – which had supported Mr Morsi’s removal – said it was withdrawing from talks to choose an interim prime minister, describing the shooting incident as a “massacre”.
‘Weapons seized’
Both the Brotherhood and the Egyptian health ministry said at least 40 people had been killed, including an army officer.
Some 300 people were reported to be wounded.
TV channels broadcast images of dead and injured people being taken to a makeshift hospital in the Rabaa al-Adawiya mosque, where Brotherhood supporters have been based.
But there were conflicting reports over how the violence unfolded.
The Muslim Brotherhood said the army had raided its sit-in at about 04:00 (02:00 GMT) as protesters were performing dawn prayers.
“The protesters were taken unawares and the troops used live ammunition, bird shot and tear gas,” protester Alaa el-Hadidi told the BBC.
“The thugs came from the side. We were the target,” he told AFP.
The Freedom and Justice Party, the Brotherhood’s political wing – which took nearly half the seats in last year’s historic election – called on Egyptian’s to stage an “uprising” in response to the incident, against “those trying to steal their revolution with tanks”.
It also urged “the international community and international groups and all the free people of the world to intervene to stop further massacres” and to stop Egypt becoming “a new Syria”.
But in a statement read on state media, the army blamed the shooting on “an armed terrorist group” that had tried to storm the barracks.
It said an army officer was among those killed and that a number of others were wounded, some critically.
The statement said some 200 people had been arrested and were found to have weapons, ammunition and petrol bombs.
The BBC’s Jim Muir in Cairo says that despite the conflicting reports, it is clear that blood has been shed, which will aggravate an already critical situation.
The withdrawal of the ultra-conservative Nour party from the political transition talks will also set back efforts to appoint a new prime minister, our correspondent adds.
Party spokesman Nadder Bakkar said it had “decided to withdraw immediately from all negotiations in response to the massacre”.
Though the Islamist party had backed the army-led “roadmap” to new elections, it had blocked the appointment of two potential prime ministers because of concerns over the shape of a new constitution.
Morsi was replaced on Thursday by Adly Mansour – the head of the Supreme Constitutional Court. He has pledged to hold elections soon, but has as yet given no date for them.
The army has insisted it does not want to remain in power.
On Sunday, tens of thousands of both supporters and opponents of Morsi rallied in many Egyptian cities.
Source: The Daily Star