An early morning attack on a Muslim Brotherhood sit-in killed at least 40 people on Monday morning, taking the political conflict in Egypt to a disturbing new level. There have been many conflicting reports about how the incident started, who was responsible, and how many people were actually hurt, but there seems to be little doubt that around 3:30 a.m. local time, police or military forces opened fire on supporters of deposed president Mohammed Morsi, who had gathered outside the Republican Guard headquarters in Cairo. Muslim Brotherhood groups says they were unarmed and staging a peaceful sit-in, while military sources claim "terrorists" had stormed the building where Morsi is reportedly being held.

There was even some debate about what weapons were used and if the army deployed live ammunition, but evidence on the ground suggests they were indeed using deadly (or potentially deadly) weapons. This YouTube video even captured government forces shooting at protesters from nearby rooftops, as well as filming the incident themselves. (Warning: Video may disturbing for some.)

The Egyptian health ministry says 42 people were killed, but MB spokespeople put the number of injured as high as 500, calling the attack a "bloodbath" and a "massacre." The incident would be the deadliest since protestors took to the streets more than a week ago to demand Morsi's resignation. Opposition leader Mohamed ElBaradei condemned the latest round of violence.

The violence also threatens to turn what began as a peaceful outpouring of political protest into a full-scale civil war. The assault has already derailed talks to form a new coalition government and hold new elections, as the second-biggest Islamist party, Al Nour, has now withdrawn from the negotiations. Muslim Brotherhood leaders have also called for Egyptians to rise up against the military, before it Egypt becomes "a new Syria."

Despite the deaths, there seems to be little sympathy for the Muslim Brotherhood, given their disastrous reign of the last year, but others recognize the danger of the army — which claims it was protecting the people and not grabbing power for itself when it arrested Morsi — firing on its own citizens.

Meanwhile, the headquarters of the MB was closed after police claimed more weapons were found inside. More clashes between demonstrators and the army are expected before the day is over.