CAIRO -- Opponents of President Mohamed Morsi were reported to have set fire to his party's offices in several Egyptian cities on Friday in a spasm of protest and clashes after he granted himself broad powers above any court declaring himself the guardian of Egypt's revolution, and used his new authority to order the retrial of Hosni Mubarak.
In the Mediterranean city of Alexandria, the opponents of the Muslim Brotherhood's Freedom and Justice Party clashed with followers of Mr. Morsi, an Islamist, who won Western and regional plaudits only days ago for brokering a cease-fire to halt eight days of lethal exchanges between Israeli forces and militants in the Gaza Strip.
Mr. Morsi, Egypt's first democratically elected president, portrayed his decree assuming the new powers as an attempt to fulfill popular demands for justice and protect the transition to a constitutional democracy. He said it was necessary to overcome gridlock and competing interests. But the unexpected breadth of the powers he seized raised immediate fears that he might become a new strongman.
"We are, God willing, moving forward, and no one stands in our way," Reuters quoted Mr. Morsi as saying on Friday said in a suburban mosque here after Friday prayers.
"I fulfill my duties to please God and the nation and I take decisions after consulting with everyone," he said. "Victory does not come without a clear plan and this is what I have."
He spoke as state television reported that his party's offices in the Suez Canal cities of Suez, Port Said and Ismailia had been burned as his foes rampaged. Thousands of people protesting Mr. Morsi's power grab gathered in Tahrir Square here -- the focal point of protests that, last year, swept away Mr. Mubarak. Elsewhere in the capital, the president's supporters massed in even larger numbers outside the presidential palace where Mr. Morsi said his aim was "to achieve political, social and economic stability."
"I am for all Egyptians. I will not be biased against any son of Egypt," he said on a stage outside the presidential palace, Reuters, reported, adding he was working for social and economic stability. "Opposition in Egypt does not worry me, but it has to be real and strong," he said.
Sounding defensive at times and employing some of the language favored by his autocratic predecessor, Mr. Morsi justified his power grab as necessary to move Egypt's revolution forward.
"The people wanted me to be the guardian of these steps in this phase," he said, reminding his audience that he was freely elected after a contest "that the whole world has witnessed."
"I don't like, and don't want -- and there is no need -- to use exceptional measures," he said. "But those who are trying to gnaw the bones of the nation," he added, "must be held accountable."
News reports said clashes spread from Alexandria to the southern city of Assyut. But the severity of the clashes was not immediately clear.
Mr. Morsi's new powers prompted one prominent adversary, Mohamed ElBaradei, to say on Twitter: "Morsi today usurped all state powers & appointed himself Egypt's new pharaoh."
"An absolute presidential tyranny," Amr Hamzawy, a liberal member of the dissolved Parliament and prominent political scientist, wrote in an online commentary. "Egypt is facing a horrifying coup against legitimacy and the rule of law and a complete assassination of the democratic transition."
Mr. Morsi issued the decree on Thursday at a high point in his five-month-old presidency, when he was basking in praise from the White House and around the world for his central role in negotiating a cease-fire that the previous night had stopped the fighting in the Gaza Strip.
But his political opponents immediately called for demonstrations on Friday to protest his new powers. "Passing a revolutionary demand within a package of autocratic decisions is a setback for the revolution," Abdel Moneim Aboul Fotouh, a more liberal former leader of the Muslim Brotherhood and a former presidential candidate, wrote online. And the chief of the Supreme Constitutional Court indicated that it did not accept the decree.
In Washington on Thursday, the State Department spokeswoman, Victoria Nuland, released a statement saying: "The decisions and declarations announced on November 22 raise concerns form many Egyptians and the international community," and noting that "one of the aspirations of the revolution was to ensure that power would not be overly concentrated in that hands of any one person or institution." The statement called for resolution "through democratic dialogue."
Mr. Morsi's advisers portrayed the decree as an effort to cut through the deadlock that has stalled Egypt's convoluted political transition more than 20 months after President Mubarak's ouster. Mr. Morsi's more political opponents and the holdover judicial system, they argued, were sabotaging the transition to thwart the Islamist majority.
The liberal and secular opposition has repeatedly threatened to boycott the Islamist-dominated constitutional assembly. (It is led by Mr. Morsi's allies in the Freedom and Justice Party. Members were picked by Parliament, where Islamists won a nearly three-quarters majority.) And as the assembly nears a deadline set under an earlier interim transition plan, most secular members and the representatives of the Coptic Church have walked out, costing it up to a quarter of its 100 members and much of its legitimacy.
Meanwhile, the Supreme Constitutional Court -- which Mr. Mubarak had tried to stack with loyalists and where a few judges openly fear Islamists -- is poised to issue a decision that could dissolve the current assembly and require a new one. Another court already dissolved an earlier assembly and, on the eve of Mr. Morsi's election in June, the Constitutional Court dissolved Parliament, citing technical issues of eligibility.
After the dissolution of Parliament, leaders of the council of generals who had ruled since Mr. Mubarak's ouster seized all legislative power and control of the budget.
But in August, Mr. Morsi won the backing of many other generals and officers for a decree that returned the army to its barracks and left him in sole control of the government, with executive and legislative authority.
Thursday's decree frees Mr. Morsi, his decrees and the constitutional assembly from judicial oversight as well.
In a television interview, Mr. Morsi's spokesman, Yasser Ali, stressed that the expanded powers would last only until the ratification of a new constitution in a few months, calling the decree "an attempt to end the transitional period as soon as possible."
"Going around in a vicious circle in a transitional period has to end," he said, apparently referring to the deadlocked constitutional assembly. In some respects, Mr. Morsi's decree fulfills opposition demands. Secular representatives in the constitutional assembly had walked out in part over their accusation that the Islamists were unfairly rushing the work. But the decree pushes the deadline back two months from the end of the year.
Mr. Morsi also replaced the public prosecutor, Abdel Meguid Mahmoud, a Mubarak appointee widely criticized for failing to win stronger sentences against Mr. Mubarak and his associates, and against abusive police officers. (Mr. Mubarak was sentenced to life in prison for overseeing the killing of protesters, but the verdict found no direct evidence of his involvement, paving the way for an appeal.)
Mr. Mahmoud's replacement is Talaat Ibrahim Abdullah, former leader of the movement for judicial independence under Mr. Mubarak.
Mr. Morsi ordered retrials for Mr. Mubarak and others accused of responsibility for killing civilian protesters during the uprising. He stripped the accused of protections against being tried twice for the same crime and issued a law setting up a new transitional legal system to handle the retrials.
Another decree provision granted the president the "power to take all necessary measures and procedures" against any potential threat to the revolution.
On the Web site of the state newspaper Al Ahram, a prominent jurist, Salah Eissa, urged citizens "to take to the street and die, because Egypt is lost," adding, "immunizing the decisions of the president with a constitutional declaration is a forgery and a fraud."
Nathan J. Brown, a scholar of the Egyptian legal system at George Washington University, summed up the overall message: "I, Morsi, am all powerful. And in my first act as being all powerful, I declare myself more powerful still. But don't worry -- it's just for a little while."
David D. Kirkpatrick and Kareem Fahim reported from Cairo and Alan Cowell from Paris. Mayy El Sheikh contributed reporting.
This article originally appeared in The New York Times.