On a day that was already expected to bring tension and possible violence to the streets of Egypt, a government prosecutor has ordered that ousted President Mohamed Morsi be detained for 15 days, on accusations that he collaborated with terrorists to kill police officers and soldiers. The charges stem from Morsi's 2011 prison break after he was arrested during protests against then-President Hosni Mubarak. He is accused of conspiring with members of the Palestinian militant group Hamas to set fire to the prison, kidnapping police officers and soldiers, and killing some guards and other prisoners.

Morsi has already been detained since July 3 when Egypt's military leaders ordered him removed from office in the not-coup that really was a coup. The military has previously said that he was merely being detained for his own safety, but now they are threatening to charge him with several serious crimes, much as Mubarak was when he was removed from power.

The decision has angered Morsi's Muslim Brotherhood supporters who were already on edge ahead of Friday's day of planned protests. Earlier in the week, the army's top general, Abdel Fattah El Sisi called for mass protests to be directed against "terrorists," which would also give him the mandate to crack down those who are committing violence. It was a call that most interpreted as a threat against the Brotherhood, which is the nation's largest Islamist party. Brotherhood supporters are planning their own counter-protests that are now likely to be fueled by outrage over the charges against Morsi.

Friday is traditionally the largest day for demonstrations in Tahrir Square, and today's could be the most contentious since Morsi's overthrow, as military troops are already gathering in the Square.