Egyptian President Mohamed Morsi issued a new constitutional declaration on Thursday in which he assumed sweeping powers that will not be subject to appeal.

And in a move likely to inflame a standoff with the country's judiciary, he sacked prosecutor general Abdel Meguid Mahmud, whom he failed to oust last month, appointing Talaat Ibrahim Abdallah to replace him.

"The president can issue any decision or measure to protect the revolution," according to the constitutional declaration, read out on television by spokesman Yasser Ali.

"The constitutional declarations, decisions and laws issued by the president are final and not subject to appeal."

He also said no judicial body can dissolve the Islamist-dominated constituent assembly that is writing a new constitution and which has been criticised by the secular-minded opposition for failing to represent all segments of society.