Egypt's presidency on Tuesday rejected an army ultimatum threatening to intervene if Islamist President Mohamed Morsy did not meet the demands of the people, raising the stakes in the country's political crisis.
The army statement, read out on television Monday, had given Morsy 48 hours to comply with its call.
"If the demands of the people are not met in this period…[the armed forces] will announce a future roadmap and measures to oversee its implementation," it said.
But in a statement issued overnight, the presidency insisted it would continue on its own path towards national reconciliation.
The army declaration had not been cleared by the presidency and could cause confusion, it said.
The presidency also denounced any declaration that would "deepen division" and "threaten the social peace."
Morsy was consulting "with all national forces to secure the path of democratic change and the protection of the popular will," it added.
"The civil democratic Egyptian state is one of the most important achievements of the 25 January revolution," said the presidency, referring to the 2011 uprising that toppled dictator Hosni Mubarak.
"Egypt will absolutely not permit any step backward whatever the circumstances," it added.
The army's statement came just a day after millions of protesters took to the streets across Egypt Sunday, calling for Morsy to step down.
It received a rapturous welcome from Morsy's opponents, still camped out in Cairo's Tahrir Square.
Tamarod, the grass-roots campaign behind Sunday's massive protests against Morsy, also hailed the statement by the armed forces which it said had "sided with the people."
It "will mean early presidential elections," Tamarod's spokesman Mahmoud Badr told reporters.
Tens of thousands of jubilant protesters poured into the streets of Cairo, Alexandria and other large cities after the statement was broadcast. Raucous cheers rang out across main squares.
In Tahrir, protesters voiced their support for army chief and Defence Minister General Abdel Fattah al-Sisi, chanting: "Come down Sisi, Morsy is not my president."
The army, which led a tumultuous transition after the 2011 revolt that ousted Mubarak, had given all parties one week to reconcile their differences.
"This week, there has been no sign of gestures or acts," the army statement said.
"Wasting more time will lead only to more division…which we have warned and continue to warn against."
Egypt has been deeply divided between Morsy's Islamist supporters and a broad-based opposition.
The huge turnout for Sunday's protests, which the military put at millions nationwide, handed the initiative to the opposition Tamarod movement.
Tamarod had issued its own ultimatum, giving Morsy until 5 pm (3 pm GMT) on Tuesday to quit or face an open-ended campaign of civil disobedience.
But the army statement significantly increased the stakes.
Sixteen people died in protests on Sunday, including eight in clashes between supporters and opponents of the president outside the Cairo headquarters of the Muslim Brotherhood, to which Morsy belongs, the health ministry said.
Early on Monday, protesters set the Brotherhood's headquarters ablaze before looting it.
"This is a historic moment. The Brotherhood ruined the country, so stealing from them is justified," one man said.
A senior government official told AFP that four ministers — tourism, environment, communication and legal affairs — had tendered their resignations to Prime Minister Hesham Qandil.
Tamarod — Arabic for rebellion — is a grassroots campaign which says it has collected more than 22 million signatures to a petition demanding new elections.
On Sunday, opposition leader Hamdeen Sabbahi urged military intervention if Morsy refused to quit, stressing however that the best outcome would be for him to step down of his own accord.
Morsy's opponents accuse him of having betrayed the revolution by concentrating power in Islamist hands and of sending the economy into freefall.
His supporters say he inherited many problems from a corrupt regime, and that he should be allowed to complete his term, which ends in 2016.
But the counter-demonstrations they organised in the run-up to Sunday's protests failed to draw the numbers that the opposition brought out onto the streets.
US President Barack Obama, whose government is a major military aid donor to Egypt, called on Morsy's government to reach out to the opposition.
"What is clear right now is that although Mr. Morsy was elected democratically, there is more work to be done to create the conditions in which everybody feels their voices are heard," he said.
State Department spokesman Patrick Ventrell stressed: "We don't take sides, we don't have a particular party or group or interest that we're backing."
The United Nations warned that what happened in Egypt would have a bearing on other that toppled authoritarian governments during and after the 2011 Arab Spring.
"What Egypt does with its transition will have a significant impact on other transition countries in the region," said UN deputy spokesman Eduardo del Buey.