CAIRO (AP) — Thousands of opponents of Egypt's Islamist president clashed with his supporters in cities across the country Friday, burning several offices of the Muslim Brotherhood, in the most violent and widespread protests since Mohammed Morsi came to power, sparked by his move to grant himself sweeping powers.

The violence, which left 100 people injured, reflected the increasingly dangerous polarization in Egypt over what course it will take nearly two years after the fall of autocrat Hosni Mubarak.

Critics of Morsi accused him of seizing dictatorial powers with his decrees a day earlier that make him immune to judicial oversight and give him authority to take any steps against "threats to the revolution". On Friday, the president spoke before a crowd of his supporters massed in front of his palace and said his edicts were necessary to stop a "minority" that was trying to block the goals of the revolution.

"There are weevils eating away at the nation of Egypt," he said, pointing to old regime loyalists he accused of using money to fuel instability and to members of the judiciary who work under the "umbrella" of the courts to "harm the country."

Clashes between his opponents and members of Morsi's Muslim Brotherhood erupted in several cities. In the Mediterranean city of Alexandria, anti-Morsi crowds attacked Brotherhood backers coming out of a mosque, raining stones and firecrackers on them. The Brothers held up prayer rugs to protect themselves and the two sides pelted each other with stones and chunks of marble, leaving at least 15 injured. The protesters then stormed a nearby Brotherhood office.

State TV reported that protesters burned offices of the Brotherhood's political arm in the Suez Canal cities of Suez, Ismailia and Port Said, east of Cairo.

In the capital Cairo, security forces pumped volleys of tear gas at thousands of pro-democracy protesters clashing with riot police on streets several blocks from Tahrir Square and in front of the nearby parliament building.

Tens of thousands of activists massed in Tahrir itself, denouncing Morsi and chanting "Leave, leave" and "Morsi is Mubarak ... Revolution everywhere." Many of them represented Egypt's upper-class, liberal elite, which have largely stayed out of protests in past months but were prominent in the streets during the anti-Mubarak uprising that began Jan. 25, 2011.

"We are in a state of revolution. He is crazy of he thinks he can go back to one-man rule," one protester, Sara Khalili, said of Morsi.

"If the Brotherhood's slogan is 'Islam is the solution' ours is 'submission is not the solution'," said Khalili, a mass communications professor at the American University in Cairo. "God does not call for submission to another man's will."

Frustration had been growing for months with Morsi, Egypt's first freely elected president, who came to office in June. Critics say the Muslim Brotherhood, from which he hails, has been moving to monopolize power and that he has done little to tackle mounting economic problems and continuing insecurity, much less carry out deeper reforms.

Morsi's supporters, in turn, say he has faced constant push-back from Mubarak loyalists and from the courts, where loyalists have a strong presence. The courts have been considering a string of lawsuits demanding the dissolution of the Islamist-dominated assembly writing the next constitution. The courts already dissolved a previous version of the assembly and the Brotherhood-led lower house of parliament.

Morsi made his move Thursday, at a time when he was bolstered by U.S. and international praise over his mediating of a cease-fire ending a week of battles between Israel and Hamas in Gaza. Only a day earlier, Morsi had met with U.S. Secretary of State Hillary Rodham Clinton just before the truce was announced.

Mustafa Kamel el-Sayyed, a Cairo University political science professor, said Morsi may be confident that the U.S. won't pressure him on his domestic moves. "The U.S. administration is happy to work with an Islamist government (that acts) in accordance with U.S. interests in the region, one of which is definitely the maintaining of the peace treaty between Egypt and Israel" and protecting Israel's security.

U.S. State Department spokeswoman Victoria Nuland said Friday that Morsi's declarations "raise concern for many Egyptians and for the international community."

The U.S. calls for Egyptians to "resolve their differences over these important issues peacefully and through democratic dialogue," she said.

On Thursday, Morsi unilaterally issued amendments to the interim constitution that made all his decisions immune to judicial review or court orders. He gave similar protection to the constitutional panel and the upper house of parliament, which is dominated by the Brotherhood and also faced possible disbanding by the courts.

Morsi, who holds legislative as well as executive powers, also declared his power to take any steps necessary to prevent "threats to the revolution," public safety or the workings of state institutions. Rights activists warned that the vague — and unexplained — wording could give him even greater power than those Mubarak held under emergency laws throughout his rule.

The decree would be in effect until a new constitution is approved and parliamentary elections are held, not expected until the Spring.

The state media described Morsi's decree as a "corrective revolution," and supporters presented the move as the only way to break through the political deadlock preventing the adoption of a new constitution.

Amnesty International said the new powers "trample the rule of law and herald a new era of repression." It said a new "law protecting the revolution" also announced Thursday could provide for detaining people for up to six months without charge.

Prominent Egyptian democracy activist Mohamed ElBaradei called Morsi a "new pharaoh." The president's one-time ally, the April 6 movement, warned that the polarization could bring a "civil war."

One of Morsi's aides, Coptic Christian thinker Samer Marqous, resigned to protest the "undemocratic" decree.

"This is a crime against Egypt and a declaration of the end of January revolution to serve the interest of the Muslim Brotherhood dictatorship," wrote Ibrahim Eissa, chief editor of daily Al-Tahrir. "The revolution is over and the new dictator has killed her."

In front of the presidential palace, Muslim Brotherhood supporters and other Islamists chanted "the people support the president's decree," pumping their fists in the air.

"God will humiliate those who are attacking our president, Mohammed Morsi," said ultraconservative cleric Mohammed Abdel-Maksoud. "Whoever insults the sultan, God humiliates him," he added.

In rival protests in the southern city of Assiut, ultraconservative Islamists of the Salafi tend and former Jihadists outnumbered liberal and leftists, such as the April 6 youth groups. The two sides exchanged insults and briefly scuffled with firsts and stones.

With his decrees, Morsi was playing to widespread discontent with the judiciary. Many — even Brotherhood opponents — are troubled by the presence of so many Mubarak era-judges and prosecutors, who they say have failed to strongly enough prosecute the old regime's top officials and security forces for crimes including the killing of protesters.

In his decrees, Morsi fired the controversial prosecutor general and created "revolutionary" judicial bodies to put Mubarak and some of his top aides on trial a second time for protester killings. Mubarak was sentenced to life in prison for failing to stop police from shooting at protesters, but many were angry he was not found guilty of actually ordering the crackdown during the uprising against his rule.

In his speech Friday. Morsi told supporters that his decisions were meant to stop those "taking shelter under judiciary."

He said the courts had been about to disband the upper house of parliament.

"This is minority but they represent a threat to the revolution's goals," he said. "It is my duty, if I see this, to go forward along the path of the revolution and prevent any blockage."