The Egyptian president, Mohamed Morsi, has said he will not step down as demanded by millions of protesters, vowing to protect his "constitutional legitimacy" with his life.
The army on Tuesday also reiterated that its initial statement on Monday was not a de facto "coup".
"The doctrine and culture of the Armed Forces do not allow the adoption of any 'military-coup-based' policies. The Egyptian military always stands by the will and aspirations of the glorious Egyptian people for change and reform.
"The aim of the Armed Forces' statement is to push all political parties nationwide to quickly find solutions for the current crisis and reach a formula of national compromise that complies with the demands of the Egyptian people."
In response to the army deadline, Muslim Brotherhood spokesman Mohamed al-Beltagui urged Morsi’s supporters to stand ready to sacrifice their lives to prevent a coup.
"Seeking martyrdom to prevent this coup is what we can offer to the previous martyrs of the revolution," he said in a statement, a reference to more than 800 people killed during the 2011 uprising against Hosni Mubarak.