The head of the Egyptian military has warned that political conflict in the country could lead to the collapse of the state.
General Abdel Fattah al-Sisi, who is also Egypt's defence minister, warned: "The continuation of the struggle of the different political forces ... over the management of state affairs could lead to the collapse of the state."
He also said that protecting the Suez Canal - a vital shipping route - was one of the main aims of the army deployment in the cities shaken by violence over the last week.
President Mohamed Mursi has declared a state of emergency and a curfew in three Suez Canal cities, after continued violence responding to the sentencing to death of 21 people for their role in deadly rioting at a football stadium in Port Said last February.
Wherever there is division in Egypt right now – death seems sure to follow. The greatest toll came amid gunfire and tear gas in Port Said.
Riots sparked by death sentences passed in connection with last year's deadly riot at the Port Said football stadium have killed 22 people.