CAIRO -- The Muslim Brotherhood early Tuesday called on its supporters to take to the streets to protect the “legitimacy” of President Mohammed Morsi after a second day of massive protests demanded the resignation of the country’s first democratically elected president.

Within minutes of the Brotherhood issuing its summons, pro- and anti-Morsi demonstrators reportedly clashed in Mahala in the Nile Delta, and pro-Morsi crowds were reported assembling in Giza, an impoverished Cairo district, to march on anti-Morsi crowds in Tahrir Square, a 10-minute walk away.

Pro-Morsi crowds also headed for the presidential palace, where tens of thousands of anti-Morsi demonstrators have held sway for two days.

Gehad El-Haddad, the Brotherhood’s spokesman, used his Twitter feed to urge Egyptians to “go to the streets all across the country in refusal of any attempted coup,” a reference to the military’s ultimatum, delivered Monday, giving the Morsi government and its opponents 48 hours to resolve their differences or the military would “intervene” in the conflict.

“We call for respect for the democratically elected choice of the ppl,” El-Haddad tweeted, using the hash tags #National Coalition for #Legitimacy.

At 1:30 a.m. Morsi's office issued a statement saying that it had not approved the military's 48-hour deadline and that the president continued to see himself as Egypt's legitimate leader.

"The president continues to hold consultations with all national forces in order to secure the path of democratization and the protection of the popular will."

The sudden appearance of Brotherhood supporters on the streets added new tension to a country already stretched taut by the gigantic outpouring of anti-Morsi sentiment that brought as many as 14 million people into the streets on Sunday, marking Morsi’s first anniversary in office with demands that he resign.

The country’s military added to that tension Monday when it had a statement read on state television setting the 48-hour deadline for a resolution and warning that if it were not met, the military would dictate a “roadmap” for a solution.

The statement set off jubilation among many in the crowds who thought the announcement meant that Morsi would have to go. But the military did not say what its roadmap might require or what steps it would take to enforce it.

The early Tuesday call for Brotherhood supporters to take to the streets made clear that Morsi and his backers would not go quietly. Instead, they insisted that the process that saw him elected over 13 other candidates must be respected.

“We condemn some opposition for resorting to violence as a means of political expression,” El-Haddad tweeted.

It was a dramatic end to a 24-hour period that had begun with hundreds of thousands of protesters chanting “Morsi Ir-hal,” Arabic for leave, and portended violent clashes in the hours and days ahead.

In Cairo’s iconic Tahrir Square, in scenes reminiscent of the 2011 uprising that led to the fall of former Egyptian leader Hosni Mubarak, thousands celebrated as though Morsi had already resigned. Car horns, fireworks and chants were so loud that it was at times deafening – and with no sign of letting up, despite conflicting statements from an increasingly fractured opposition of how it should respond next.