CAIRO, July 3 - Egyptian President Mohamed Mursi vowed to stay in power and defend constitutional legitimacy on Wednesday as generals worked on plans to push the Islamist aside within the day and suspend the constitution.

Protesters opposing Egyptian President Mohamed Mursi shout slogans near a banner with pictures of Muslim Brotherhood members during a demonstration in front of the Presidential Palace "Qasr Al Quba" in Cairo July 2, 2013.[Photo/Agenceis]

In a defiant midnight television address responding to military demands that he share power with his opponents or see the army impose its own solution, Mursi warned that any deviation from the democratic order approved in a series of votes last year would lead Egypt down a dangerous path.

He was speaking as vast crowds of protesters rallied in central Cairo and across the nation to demand the Muslim Brotherhood politician's resignation in a third night of mass demonstrations. His supporters also turned out and some were involved in clashes with security forces at Cairo University.

"The price of preserving legitimacy is my life," Mursi said in an impassioned, repetitive, 45-minute ramble. "Legitimacy is the only guarantee to preserve the country."

In a warning aimed as much at his own militant supporters as at the army, he said: "We do not declare jihad (holy war) against each other. We only wage jihad on our enemies."

Urging Egyptians not to heed the siren calls of what he called remnants of the former authoritarian regime, "the deep state" and the corrupt, he said: "Don't be fooled. Don't fall into the trap. Don't let them steal your revolution."

An opposition spokesman called Mursi's defiance "an open call for civil war". Peaceful protests would go on, he said.

On Monday, army commander General Abdel Fattah al-Sisi gave Mursi 48 hours to reach an accommodation with his opponents. Otherwise, he said, the military would step in and implement its own roadmap for the country's future.

A military spokesman said the armed forces would not comment on the president's statement until Wednesday afternoon. The deadline is set to expire at 5 pm. (1500 GMT).

Condemning a coup against their first freely elected leader, tens of thousands of Muslim Brotherhood supporters took to the streets, clashing with opponents in several towns. But they were dwarfed by anti-government protesters who turned out in their hundreds of thousands across the nation.

Security sources said dozens of people were wounded in the clashes at Cairo University involving Mursi supporters. Witnesses heard gunfire and teargas was used by the authorities.