The Egyptian president's national security adviser said on Wednesday that a "military coup" was under way and army and police violence was expected to remove pro-Mursi demonstrators.
"In this day and age, no military coup can succeed in the face of sizeable popular force without considerable bloodshed," said Essam El-Haddad, adding it might be his last post on his official Facebook page.
Egypt's armed forces and Islamist President Mohamed Mursi refused to back down on Wednesday as a deadline for a military takeover passed with rival demonstrators out in force in the streets of Cairo.
"There are still people in Egypt who believe in their right to make a democratic choice. Hundreds of thousands of them have gathered in support of democracy and the presidency. And they will not leave in the face of this attack. To move them, there will have to be violence," said Haddad.
Egyptian authorities have placed an international travel ban on the president and other leading members of the Muslim Brotherhood, security sources told Reuters.