He said the Brotherhood would go ahead with planned demonstrations Friday in Cairo followed by an indefinite sit-in.
If the sit-in extends to Sunday, it would coincide with mass demonstrations planned by opposition factions in front of the presidential palace.
Governments around the world are paying attention -- at the least, to make sure that their own workers and citizens are safe.
About 200 U.S. Marines in Sigonella, Italy, and Moron, Spain, have been put on alert as a precaution, according to two officials in President Barack Obama's administration.
The units have several V-22 tilt-rotor aircraft that could carry personnel and weapons to protect the U.S. Embassy and American government personnel and citizens if violence breaks out targeting Americans. They've been told to be ready to be airborne within 60 minutes of getting orders to deploy, the officials said.
The United States has approved the departure of embassy and consulate employees and their dependents because of the brewing unrest, a senior State Department official said. Nonessential employees and their relatives can get help leaving, if they choose to do so.