Dozens of supporters of ousted President Mohammed Morsi are reported to have been killed at a demonstration in Egypt.
The latest number, according to Reuters, citing state TV, is 42.
Accounts vary of what exactly happened.
A statement from the Muslim Brotherhood said its members were merely praying at a sit-in outside of a Presidential Guard Barrack, according to the BBC.
The army, on the other hand, says they were trying to storm the barracks.
Either way, this could lead to a major escalation in an already unstable situation.
Morsi's Freedom and Justice Party has already called for an "uprising" based on the incident.
This video (posted by Al-Jazeera) purports to show teargas being fired at Morsi supporters.
Tweets from reporters on the ground give a further sense of what happened.
Egyptian massacre: two witnesses say the attack began at dawn prayer, the Islamists protestors were unarmed, ran in panic
— David D. Kirkpatrick (@kirkpatricknyt) July 8, 2013
All of those interviewed were clear that the shooting started as the protesters' mass dawn prayers were coming to a close.
— Patrick Kingsley (@PatrickKingsley) July 8, 2013