(Anti-Morsi protestors in June/Wikimedia Commons)

UPDATE 1:30 PM: Health officials report that the death toll in Cairo has risen to 51.

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Egyptian soldiers reportedly opened fire on hundreds of supporters of ousted president Mohamed Morsi who had gathered to pray outside the facility where they believe he is being held.

The death toll has now climbed to 40 and about 300 people were injured in the shooting, the Washington Post reported. However Mahmoud Zaqzooq, a Muslim Brotherhood spokesman, said 53 were shot dead, including five children.

The details remain murky, as Egypt's military insists that a terrorist group attacked the protesters outside the Republican Guard headquarters, according to the Daily Beast. The military also said armed assailants fired on the soldiers first.

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Brotherhood officials and dozens of witnesses said troops opened fire as the protesters were embarking upon a peaceful dawn prayer. But a military spokesman said an armed group from the pro-Morsi camp attacked troops around the headquarters, leading to one soldier’s death, and that the military was forced to respond.

Differing eyewitness accounts describe a pro-Morsi protestor firing what appeared to be a homemade handgun at advancing soldiers, but hours after the initial attack began. Another witness said he saw two other pro-Morsi protestors with similar weapons.

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The Brotherhood’s Freedom and Justice party issued a statement calling for an “uprising against those who want to steal the revolution with tanks” and asking the world to prevent a “new Syria.”

The shooting was the single deadliest attack since the 2011 revolution that toppled longtime autocratic leader Hosni Mubarak, said the New York Times.

Read more at The Daily Beast, Washington Post and The New York Times

See all of Neon Tommy's coverage on Egypt