Egypt's army chief has said political strife is pushing the state to the brink of collapse, as the country’s first elected leader struggles to contain bloody street violence.

General Abdul Fattah al-Sisi said that one of the primary goals of deploying troops in cities on the Suez Canal was to protect the waterway that is vital for Egypt's economy and world trade.

The comments, published on an official army Facebook page, followed 52 deaths in the past week of disorder and highlighted the mounting sense of crisis facing Egypt.

President Mohammed Mursi is struggling to fix a teetering economy and needs to prepare Egypt for a parliamentary election in a few months that is meant to cement the new democracy.

The comments are unlikely to mean the army wants to take back the power it held.

However, it sends a powerful message that Egypt's biggest institution is worried about the fate of the nation after five days of turmoil in major cities.

"The continuation of the struggle of the different political forces ... over the management of state affairs could lead to the collapse of the state," said General Sisi, who is also defence minister in the government Mr Mursi appointed.

He said the economic, political and social challenges facing the country represented "a real threat to the security of Egypt and the cohesiveness of the Egyptian state" and the army would remain "the solid and cohesive block" on which the state rests.

Political opponents spurned a call by Mr Mursi for talks yesterday to try to end the violence.

Instead, huge crowds of protesters took to the streets in Cairo and Alexandria, and in the three Suez Canal cities - Port Said, Ismailia and Suez - where Mr Mursi imposed emergency rule and a curfew on Sunday.

Residents in the three canal cities demonstrated overnight in defiance of the curfew.

At least two men died in fighting in Port Said, raising to at least 42 people who have now been killed there, most of them by gunshot wounds.

Protests first flared to mark the second anniversary of the uprising that erupted on 25 January, 2011 and toppled Hosni Mubarak 18 days later.

They have been exacerbated by riots in Port Said by residents enraged by a court ruling sentencing several people from the city to death over deadly football violence last year.