Mursi defied a demand by the armed forces chief on Monday that he agree to share power with his opponents within 48 hours or have the generals take charge. Calling the army statement misleading and divisive, he said he would stick to his own plan.

But time has all but run out for Mursi, as liberal leaders are refusing to talk to him. Opponents have been dancing in the streets since the intervention by General Abdel Fattah al-Sisi.

Military sources told reporters that, assuming the politicians failed to end a year of deadlock under Mursi before Wednesday’s 5pm (10pm Hong Kong time) deadline, the generals had their own draft programme ready to implement – though it could be fine-tuned in consultation with willing political parties.

Under the roadmap, the military would install an interim council, composed mainly of civilians from different political groups and experienced technocrats, to run the country until an amended constitution was drafted within months.

That would be followed by a new presidential election, but parliamentary polls would be delayed until strict conditions for selecting candidates were in force, the sources said.

They would not say how the military intended to deal with Mursi if he refused to go quietly. One power he might seek to exercise would be to call a referendum on continuing his term.

Some of his Islamist supporters have vowed to defend what they see as the legitimate, democratic order, even if it means dying as martyrs. And some have a history of armed struggle against the state.

The confrontation has pushed the most populous Arab nation closer to the brink of chaos amid a deepening economic crisis two years after the overthrow of Hosni Mubarak, raising concern in Washington, Europe and neighbouring Israel.

Troops intervened to break up clashes in the Mediterranean city of Alexandria. They were also out on the streets of Suez and Port Said, at either end of the Suez Canal. The waterway is vital to world trade and to Egypt’s struggling economy.

Mursi was looking increasingly isolated as ministers and officials who are not members of his Muslim Brotherhood resigned. He also lost a judicial battle when a court evicted his prosecutor-general and reinstated a Mubarak appointee.

Egypt’s Coptic Pope, spiritual leader of the country’s 10 per cent Christian minority, expressed open support for the anti-Mursi Tamarud (Rebel) movement in a tweet, voicing support for the trio of people, army and youth.

The leading Muslim religious authority, Al-Azhar, called for the will of the people to prevail peacefully.

Mursi met Sisi for a second day, his office said, along with Prime Minister Hisham Kandil. A presidential aide told the state news agency there had been no “disagreements” but there was no outward sign of a meeting of minds.

Though Mursi has held out repeated offers of dialogue, liberal opponents accuse him and the Brotherhood of bad faith and have ruled out starting talks with him before the deadline.

After that, former UN nuclear agency chief Mohamed ElBaradei will deal directly with the military on behalf of the main coalition of liberal parties. Also planning to take part are leaders of the Tamarud youth movement, which initiated mass rallies on Sunday that the army says prompted it to act.

Military sources said the armed forces would talk with the opposition National Salvation Front and other political, religious and youth organisations after the deadline.

Among figures being considered as an interim head of state was the new president of the constitutional court, Adli Mansour.

The new transition arrangements would be entirely different from the military rule that followed Mubarak’s fall and more politically inclusive, the sources said.

Then, the ruling armed forces’ council was widely criticised by liberal and left-wing politicians for failing to enact vital economic and political reforms - and for siding with the Brotherhood.

Fighting between Mursi supporters and opponents broke out in the Cairo suburb of Giza, in Alexandria and in the town of Qalyubia, north of Cairo, security sources said.

Protesters thonged Cairo’s Tahrir Square, where hovering military helicopters got loud cheers. A quarter of a million packed the square after work, celebrating wildly what they believe is Mursi’s impending departure.

Senior Muslim Brotherhood leaders branded the military ultimatum a “coup”, backed by a threat that the generals will otherwise impose their own road map for the nation.

The Brotherhood’s political wing called for mass counter- demonstrations to “defend constitutional legitimacy and express their refusal of any coup”, raising fears of violence. But the biggest pro-Mursi rally in the a Cairo suburb appeared to attract around 100,000 supporters, witnesses said.

The Brotherhood long avoided direct confrontation with the security forces despite suffering oppression under Mubarak.

After millions protested on Sunday, Sisi delighted Mursi’s opponents by effectively ordering the president to heed the demands of the street. It took the president’s office nine hours to respond with a statement indicating he would go his own way.

“The president of the republic was not consulted about the statement issued by the armed forces,” it said. “The presidency confirms that it is going forward on its previously plotted path to promote comprehensive national reconciliation ... regardless of any statements that deepen divisions between citizens.”

Describing civilian rule as a great gain from the revolution of 2011, Mursi said he would not let the clock be turned back.

The United States, which has previously defended Mursi’s legitimacy as a democratically elected leader, stepped up pressure on him to heed the mass protests but stopped short of saying he should step down.

President Barack Obama told Mursi in a phone call late on Monday that the political crisis could only be solved by talks with his opponents, the White House said. Secretary of State John Kerry hammered home the message in a call to his outgoing Egyptian colleague on Tuesday.

At least six ministers who are not Brotherhood members have tendered their resignations since Sunday, including Foreign Minister Mohammed Kamel Amr. The president’s two spokesmen and the cabinet spokesman also quit on Tuesday and nearly 150 Egyptian diplomats signed a petition urging Mursi to go.