Mursi's national security adviser said a military coup was under way as armed forces commander General Abdel Fattah al-Sisi met political, religious and youth leaders, APA reports quoting Reuters.
The state news agency MENA said they would make a joint announcement of a roadmap for a new transitional period and new elections two years after the overthrow of autocratic ex-president Hosni Mubarak in a popular uprising.
The Arab world's most populous nation has been in turmoil since the fall of Mubarak as Arab Spring uprisings took hold in early 2011, arousing concern among allies in the West and in Israel, with which Egypt has a 1979 peace treaty.
The elected Muslim Brotherhood president, in office for just a year, remained out of sight in a Republican Guard barracks surrounded by barbed wire, barriers and troops, but military sources denied media reports that he was under arrest.
"For the sake of Egypt and for historical accuracy, let's call what is happening by its real name: military coup," Mursi's national security adviser Essam El-Haddad said in a statement, warning of "considerable bloodshed" to come.
Another presidential aide, Yasser Haddara, said it was unclear whether Mursi was free to return to the palace where he spent the previous night. His message to supporters was to resist the "military coup" peacefully and not use violence against troops, police or other Egyptians.
Military chiefs, vowing to restore order in a country racked by protests over Mursi's Islamist policies, earlier issued a call to battle in a statement headlined "The Final Hours". They said they were willing to shed blood against "terrorists and fools" after Mursi refused to give up his elected office.
Armored vehicles took up position outside the state broadcasting headquarters on the Nile River bank, where soldiers patrolled the corridors and non-essential staff were sent home.
In a show of force, several hundred soldiers with armored vehicles staged a parade near the presidential palace, and security sources said Mursi and the entire senior leadership of his Muslim Brotherhood were