Egypt's Muslim Brotherhood has called for more protests Tuesday, a day after clashes between the military and supporters of ousted President Mohamed Morsi left 51 people dead.
The two sides traded blame for sparking the violence, with the Muslim Brotherhood saying the army opened fire on Morsi supporters without reason. The army says troops shot only after coming under heavy gunfire from terrorists trying to storm a military headquarters in Cairo.
Egypt's interim president Adly Mansour called for restraint from both sides and an independent investigation into the violence.
He also issued a decree Monday saying a referendum will take place within five months to ratify amendments to the country's constitution. Parliamentary elections will follow within two months, and once that chamber convenes, a date for a presidential vote will be set.
Egypt's army suspended the Islamist-drafted constitution and overthrew Morsi last week, following massive protests against his rule.
The army described the move as necessary to enforce the will of the millions of people who have repeatedly demanded his resignation. But the Muslim Brotherhood says the action was a military coup.
White House spokesman Jay Carney said Monday the U.S. is concerned by the increasing violence and what he called a "dangerous level of political polarization" in Egypt. He also said cutting off aid to Egypt would not be in Washington's best interests. Egypt is the second-largest recipient of U.S. financial assistance behind Israel.