Supporters and opponents of President Mohammed Morsi clashed Friday in the worst violence since he took office, while he defended a decision to give himself near-absolute power to root out what he called ‘‘weevils eating away at the nation of Egypt.’’

The edicts by Morsi, which were issued Thursday, have turned months of growing polarization into an open battle between his Muslim Brotherhood and liberals who fear a new dictatorship. Some in the opposition, which has been divided and weakened, were now speaking of a sustained street campaign against the man who nearly five months ago became Egypt’s first freely elected president.

The unrest also underscored the struggle over the direction of Egypt’s turbulent passage nearly two years after a popular uprising toppled Hosni Mubarak’s authoritarian regime. Liberals and secular Egyptians accuse the Brotherhood of monopolizing power, dominating the writing of a new constitution and failing to tackle the country’s chronic economic and security problems.

‘‘I don’t like, want or need to resort to exceptional measures, but I will if I see that my people, nation and the revolution of Egypt are in danger,’’ Morsi told thousands of his chanting supporters outside the presidential palace in Cairo.

But even before he spoke, thousands from each camp demonstrated in major cities, and violence broke out in several places, leaving at least 100 wounded, according to security officials.

Security forces pumped volleys of tear gas at thousands of pro-democracy protesters clashing with riot police on streets several blocks from Cairo’s Tahrir Square, birthplace of the Arab Spring, and in front of the nearby parliament building. Young protesters set fire to tree branches to counter the gas, and a residential building and a police vehicle also were burned.

Tens of thousands of activists massed in Tahrir itself, denouncing Morsi. In a throwback to last year’s 18-day anti-Mubarak uprising, they chanted the iconic slogan first heard in Tunisia in late 2010: ‘‘The people want to overthrow the regime.’’ They also yelled ‘‘erhal, erhal,’’ — Arabic for ‘‘leave, leave.’’

Outside a mosque in the Mediterranean city of Alexandria, anti-Morsi crowds threw stones and firecrackers on Brotherhood backers who used prayer rugs to protect themselves, injuring at least 15. The protesters then stormed a nearby Brotherhood office.

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

In the southern city of Assiut, ultraconservative Islamists and former jihadists outnumbered liberal and leftists in rival demonstrations. The two sides exchanged insults and scuffled briefly.

Morsi and the Brotherhood contend that supporters of the old regime are holding up progress toward democracy. They have focused on the judiciary, which many Egyptians see as too much under the sway of Mubarak-era judges and prosecutors and which has shaken up the political process several times with its rulings, including by dissolving the lower house of parliament, which the Brotherhood led.

His edicts effectively shut down the judiciary’s ability to do so again. At the same time, the courts were the only civilian branch of government with a degree of independence: Morsi already holds not only executive power but also legislative authority, since there is no parliament.

His move came at a time when he was enjoying lavish praise from U.S. President Barack Obama and Secretary of State Hillary Rodham Clinton for brokering a cease-fire between Israel and Gaza’s Hamas rulers on Wednesday. Clinton had been in Cairo for extensive talks with Morsi before the truce was announced.

U.S. State Department spokeswoman Victoria Nuland, said in a statement that the edicts raise ‘‘concerns’’ for many Egyptians and for the international community, adding that the country’s revolution had aimed in part to prevent too much power from being concentrated in one person’s hands.

The U.S. urged ‘‘all Egyptians to resolve their differences over these important issues peacefully and through democratic dialogue,’’ she said.

Amnesty International, the London-based rights group, said Morsi’s new powers ‘‘trample the rule of law and herald a new era of repression.’’

Morsi aide Samer Marqous, a Coptic Christian, resigned to protest the ‘‘undemocratic’’ decree.

‘‘Morsi’s decision means dictatorship. He creates the law, passes the law, and oversees the law,’’ said Manal Tibe, an activist who was a member of the assembly writing the new constitution until she withdrew earlier this year to protest the Islamists’ domination of it. ‘‘He is the state and the state is him.’’



Mohamed ElBaradei, Egypt’s most prominent reformer and a Nobel Peace laureate, warned that Morsi was making himself a ‘‘pharaoh’’ and appealed to him to withdraw the decrees ‘‘before the polarization and aggravation of the situation increases.’’

In his decrees, Morsi ruled that any decisions and laws he has declared or will declare are immune to appeal in the courts and cannot be overturned or halted. He also barred the judiciary from dissolving the upper house of parliament or the assembly writing the new constitution, both of which are dominated by the Brotherhood and other Islamists.

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

Morsi 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 authority than Mubarak had under emergency laws throughout his rule.

In his speech, Morsi warned of ‘‘weevils eating away at the nation of Egypt,’’ and pointed 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.’’

His supporters and other Islamists chanted, ‘‘The people support the president’s decree!’’ and pumped 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.

The state media described Morsi’s decrees as a ‘‘corrective revolution,’’ and supporters cast them as the only way to break through the political deadlock over drafting the constitution.

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,’’ including preserving the Egyptian-Israel peace deal, he said.

With his decrees, Morsi was playing to widespread discontent with the judiciary. Many — even Brotherhood opponents — contend Mubarak-era judges and officials failed to prosecute the old regime’s top officials and security forces strongly enough for crimes, including the killing of protesters.

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 the 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.

Some among Egypt’s liberal, leftist and secular forces saw the edicts as an opportunity to galvanize an opposition that has been chronically fragmented.

Sameh Makram Obeid, a leader in the liberal Dustour Party, said Morsi’s declarations are a ‘‘blessing’’ because they energized his opponents.

‘‘The solution is civil disobedience,’’ he said, echoing other activist leaders. ‘‘The separation of powers is gone completely.’’

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