Tens of thousands of protesters are defying government orders and demonstrating on the streets of Cairo as deposed Egyptian leader Mohammed Morsi is calling for a million-man march against his ouster.
The Muslim Brotherhood is not holding back in its efforts to regain power.
Former Muslim Brotherhood leader Tharwat al Khirbawi, who defected, said the group is relying on "urban jihadi doctrine" to attack police and the army.
According to al Khirbawi, the Muslim Brotherhood maintains a secret paramilitary force that will do anything, "including extreme violence to establish a Caliphate."
Tens of thousands of Brotherhood supporters chanting "Our blood and souls we sacrifice for Morsi" marched on army and security buildings late Monday. They were protesting the weekend killing of 83 Morsi supporters reportedly by the military.
"We hold the coup leaders responsible for this massacre and the bloodshed, and we demand an immediate investigation," Ahmed Aref, a Muslim Brotherhood spokesman said.
Deposed since July 3, Morsi isn't giving up. His supporters are planning a million-man march Tuesday, despite warnings by the military.
"I assure the Egyptian people that we will deal with any attempt to undermine stability very decisively," Egyptian Interior Minister Mohamed Ibrahim said.
In Washington, and across the Arab world, leaders are calling for restraint.
"Firing on your own people is unacceptable by any government. And in this situation, if it's established that this came from government sources -- it appears it did -- then we have got to make it clear to the Egyptians that's unacceptable conduct," Sen. Dick Durbin, D-Ill., said.
"We've got to try to calm things down. And for Americans at home who are saying, 'Well, why should we be interested? Five percent of the world's oil every single day goes through the Suez Canal, about 8 percent of the world trade," Mike Rogers, R-Mich., said. "So if this spills over and they lose control of Egypt, it will have real economic impacts for us at home."
Meanwhile, Egyptian police continue to arrest several key leaders of the Muslim Brotherhood and other prominent Islamist leaders.