Egypt's armed forces chief has warned the current political crisis "could lead to a collapse of the state".
General Abdul Fattah al-Sisi, in comments posted on the military's Facebook page, said such a collapse could "threaten future generations".
He made his statement following a large military deployment in three cities along the Suez Canal where a state of emergency has been declared.
More than 50 people have died in days of protests and violence.
In response, President Mohammed Morsi has cut short a planned European trip.
His spokesman said he would still visit Germany on Wednesday as planned, but the two-day trip has been cut to just a few hours and a visit to France has been cancelled.
On Monday night, thousands of people in Port Said, Ismailia and Suez - where some of the worst unrest has been - ignored a night-time curfew imposed by Mr Morsi to take to the streets.
Thousands were again on the streets of Port Said on Tuesday for the latest funerals of those killed, with mourners calling for the downfall of the president.
There were also saw continuing sporadic clashes in the capital, Cairo.
Gen Sisi's lengthy statement appears to be a veiled threat to protesters and opposition forces as well as an appeal for calm and an attempt to reassure Egyptians about the role of the military, the BBC's Yolande Knell in Cairo says.
"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," Gen Sisi, who is also Egypt's defence minister, said.
He said the economic, political and social challenges facing Egypt represented "a real threat to the security of Egypt and the cohesiveness of the Egyptian state".
The military deployment along the Suez Canal was meant only to protect the key shipping route, one of Egypt's main sources of foreign revenue, and described the army as "a pillar of the state's foundations", he added.
His comments were made in an address to army cadets which were subsequently posted on the military's official Facebook page.
Gen Sisi was appointed by President Morsi after the armed forces handed over power to him following his election in June.
He replaced Field Marshal Hussein Tantawi who had been former President Hosni Mubarak's long-time defence minister and was chairman of the ruling Supreme Council of the Armed Forces (Scaf) following his fall from power in February 2011.
The latest violence, now in its sixth day, has been focused in Port Said.
It was sparked by death sentences handed down by a court on 21 local football fans involved in riots that left 74 people dead at a football match in the city almost a year ago.
Supporters accuse the authorities of making them into scapegoats, and say security officials at last year's game between the local club, al-Masry, and the Cairo club, al-Ahly, should be held accountable for the deaths.
Protesters elsewhere have been marching in opposition to Mr Morsi's authority in the wake of the Egyptian revolution's second anniversary.
In Cairo on Tuesday police again fired tear gas at protesters near Tahrir Square, and the lobby of a major hotel close to the square was attacked, apparently by looters.
The clashes also prompted Egypt's public prosecutor to call for the arrests of a newly-formed anarchist group known as the Black Bloc.
Its black-clad members have been at the vanguard of the latest protests in Cairo. According to its Facebook page, the group is opposed only to the Muslim Brotherhood - the powerful Islamist group of which President Morsi is a member.
Mr Morsi became Egypt's first freely-elected president in last year's election.
Despite promising to form a government "for all Egyptians", he has been accused by the opposition of being autocratic and driving through a new constitution that does not adequately protect freedom of expression or religion.
His recent call for national dialogue has been rejected by his political opponents.
He had urged opposition leaders to attend a meeting on Sunday evening in an effort to calm the situation, but only Islamists already aligned with the president turned up.
Mr Morsi's supporters meanwhile accuse the opposition protesters of trying to oust a democratically elected president by undemocratic means.