EGYPT'S armed forces would suspend the constitution and dissolve Parliament under a draft political road map to be pursued if the president and the opposition fail to agree a way forward today, military sources said.

The sources said the Supreme Council of the Armed Forces (SCAF) was still discussing details and the plan, intended to resolve a political crisis that has brought millions of protesters into the streets, could be changed based on political developments.

Chief-of-staff General Abdel Fattah El-Sisi called in a statement on Monday for President Mohamed Mursi to agree within 48 hours on power-sharing with other political forces. He said the military would otherwise set out its own road map for the country's future.

Mr Mursi rebuffed the army ultimatum and the ruling Muslim Brotherhood sought to mass its supporters to defend him.

However, the Islamist leader looked increasingly isolated, with ministers resigning and the liberal opposition refusing to talk to him.

In a defiant statement, Mr Mursi's office said the president had not been consulted before the armed forces chief-of-staff set a 48-hour deadline for a power-sharing deal and would pursue his own plan for national reconciliation.

Newspapers across the political spectrum saw the military ultimatum as a turning point.

"Last 48 hours of Muslim Brotherhood rule," the opposition daily El Watan declared. "Egypt awaits the army," said the state-owned El Akhbar.

The President's office said Mr Mursi was meeting Mr El-Sisi and Prime Minister Hisham Kandil for the second straight day.

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

Military sources said troops were preparing to deploy on the streets of Cairo and other cities if necessary to prevent clashes between rival political factions.

Protesters remained encamped overnight from Monday until yesterday in Cairo's central Tahrir Square and protest leaders had called for another mass rally later in the day, dubbed a "Tuesday of persistence", to try to force the president out.

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

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

Egypt's first freely elected leader has been in office for just a year. However, many Egyptians are impatient with his economic management and inability to win the trust of non-Islamists.

The United Nations Human Rights office called on Mr Mursi to listen to the demands of the people and engage in a serious national dialogue but also said: "Nothing should be done that would undermine democratic processes."

Yesterday, US President Barack Obama called on Mr Mursi to urge him to respond to mass opposition the demonstrations and said the political crisis could only be resolved by talks.

Mr Obama also called on both sides to ensure rallies stayed peaceful after the death toll in clashes between rival protesters since Sunday reached at least 16 people.

The president of the United States, which is a big aid donor to Egypt and its military, "told President Mursi the United States is committed to the democratic process in Egypt and does not support any single party or group," the White House said.