In a statement read on state television, General Abdel Fattah al-Sisi called mass protests on Sunday, which called for President Mohamed Morsi to resign, an "unprecedented" expression of the popular will.  

"If the demands of the people are not realised within the defined period, it will be incumbent upon (the armed forces)... to announce a road map for the future," said the statement by chief-of-staff General Abdel Fattah al-Sisi.

The people had expressed their will with unprecedented clarity in the mass demonstrations and wasting more time would only increase the danger of division and violence, he said.

The army said it would oversee the implementation of the roadmap it sought "with the participation of all factions and national parties, including young people", but it would not get directly involved in politics or government.

Anti-Mursi demonstrators outside the presidential palace cheered the army statement, and the main opposition National Salvation Front, which has demanded a national unity government for months, applauded the military's move.

It was the second time in just over a week that the armed forces had issued a formal warning to the politicians, and it appeared to pile pressure on Mursi to concede power-sharing with the liberal, secular and left-wing opposition.

Cities were quiet after Sunday's mass rallies that were bigger than anything seen since the Arab Spring uprising. But the ransacking of the Brotherhood's office highlighted deepening political polarization, prompting the movement to talk of acting in self-defense.

Five non-Brotherhood government ministers tendered their resignations from the cabinet, apparently in sympathy with the protesters, underlining a sense of isolation for the party that won a series of elections last year.