In what critics are calling "a coup against legitimacy," thousands of protesters gathered throughout Egypt on Friday after President Mohamed Mursi assumed new powers that ban challenges to his decrees, laws and decisions, and bar his decisions from being revoked by any court.

Demonstrators, led by "an array of liberal and secular groups, including activists at the forefront of the protest movement that forced veteran strongman Hosni Mubarak from power early last year," gathered in Tahir Square there to protest the decree, chanting, "Mursi is Mubarak … revolution everywhere."

Mursi's decree, read on state television on Thursday, said, "The president can issue any decision or measure to protect the revolution. The constitutional declarations, decisions and laws issued by the president are final and not subject to appeal."

As Mursi's supporters—including the Muslim Brotherhood—gathered outside the presidential palace in Cairo, protesters set fire to Muslim Brotherhood offices in several cities including Port Said and Ismailia, and rival demonstrators reportedly clashed in Alexandria.

The BBC continues:

In a joint news conference on Thursday, Sameh Ashour, head of a lawyers association, and key opposition figures Mohamed ElBaradei and Amr Moussa accused Mr. Mursi of "monopolising all three branches of government" and overseeing "the total execution of the independence of the judiciary".

"We are calling on all Egyptians to protest in all of Egypt's squares on Friday," they said.

Mr. ElBaradei, a Nobel Peace Prize winner, wrote on his Twitter account that the president had "appointed himself Egypt's new pharaoh. A major blow to the revolution that could have dire consequences".

Critics say the decree is a "coup against legitimacy".

Mursi's decree will also allow retrials for people convicted of killings during Egypt's 2011 uprising, which led to Mubarak's outster, according to the BBC.