Egypt's military chief warned Tuesday the political crisis sweeping the country could lead to the collapse of the state, as thousands defied curfews and the death toll from days of rioting rose to 52.
"The continuing conflict between political forces and their differences concerning the management of the country could lead to a collapse of the state and threaten future generations," said General Abdel Fattah al-Sissi.
Sissi, who is also defence minister, warned students at a military academy that the political, economic, social and security problems constitute "a threat to the country's security and stability," according to his Facebook page.
He also vowed to defend vital infrastructure, including the Suez Canal, as medics reported another three people killed in the violence sweeping Egypt, pushing to at least 52 the death toll from five days of clashes.
The army is already deployed in the canal city of Port Said, where the worst of the bloodshed occurred in rioting triggered by death sentences passed on 21 supporters of a local football club over deadly soccer riots last year.
At the weekend, President Mohamed Morsi imposed a month-long state of emergency and curfews on the worst-hit provinces of Port Said, Ismailiya and Suez.
The Islamist-dominated Senate has since ratified a law granting the armed forces arrest powers, but Morsi's office said Tuesday he could reduce or scrap the measure if security was restored.
Thousands of demonstrators defiantly flooded the streets of the three Suez Canal cities on Monday night, chanting slogans against the Muslim Brotherhood, from which Morsi hails.
On Tuesday tear gas was fired and stones thrown in limited clashes between police and protesters around Cairo's Tahrir Square, while sporadic gunfire rang out near Port Said prison, witnesses and security sources said.
Analysts warned there was no quick fix and Morsi would have to make concessions to the opposition and protesters demonstrating against deteriorating living conditions.
"This crisis will not pass easily," said Cairo University professor Mustafa Kamel El-Sayyed.
Signup to our newsletter and follow us on Facebook and Twitter!
Sayyed said a new element had emerged on the scene: "A group of young anarchists (nicknamed as the Black Bloc) who are ready to engage in violence with the police."
But judicial sources said the prosecutor general had ordered the arrest of members of this shadowy militant group, who present themselves as defenders of protesters opposed to the president and his Islamist supporters.
"Inquiries have shown that the Black Bloc is an organised group which carries out terrorist actions," said the prosecutor's spokesman Hassan Yassine.
The prosecutor also urged "citizens to arrest anyone suspected of membership in this group and hand them over," he added.
Sissi recognised the army had a difficult task and did not want to confront citizens who have the right to protest, but insisted -- ahead of planned opposition rallies on Friday -- that "protests must be peaceful".
Opposition groups and disgruntled Egyptians accuse Morsi, the Muslim Brotherhood and other Islamists of monopolising power and say the revolution failed to reach its goals of social justice.
The violence has gained momentum since Thursday, on the eve of the second anniversary of the uprising that toppled president Hosni Mubarak and exploded on Saturday in Port Said after the death sentences were announced.
Rioters attacked police stations and the prison where the defendants were being held, sparking weekend clashes that killed 42 people.
The political dimension of the conflict hung heavily over Egypt and the crisis looked set to deepen after the National Salvation Front, a coalition of mainly liberal and leftist movements, snubbed an offer from Morsi to hold talks.
The bloc -- which demands a national salvation government and the amendment of the Islamist-drafted constitution before any talks -- urged people to "take to the streets in all Tahrir Squares on Friday to stress the sanctity of the blood of the martyrs and achieve the goals of the revolution".
The unrest highlights a deep split between Morsi's mainly Islamist allies, and an opposition of leftists, liberals, Christians and Muslims calling for freedoms and the separation of the state from religion.
Morsi postponed a visit to Paris scheduled for Wednesday, according to the French presidency. His office said a two-day visit to Berlin due to start Wednesday would be trimmed back to "only a few hours".