— The residents of this Mediterranean coastal city say their conflict with Egyptian President Mohamed Morsi started with a harsh court verdict.

Three days and 43 bodies later, the air around Port Said’s main cemetery still tinged by the stench of death, the conflict has spiraled into something much larger.

Many of the men and women who chanted for Morsi’s execution in the tense and battle-scarred streets of Port Said on Monday said that in last summer’s presidential election, they actually voted for the man.

That the city turned so vehemently against him with a single court verdict underscores Morsi’s increasing vulnerability, and suggests that others could just as easily shift their favor — potentially altering the nature of Egypt’s political divide and bringing new threats to the country’s already tenuous stability and rapidly sinking economy.

In all, at least 54 people were killed and hundreds injured across the country in four days of fighting between opposition protesters and government security forces. The clashes were set off by marches on Friday to mark the two-year anniversary of Hosni Mubarak’s ouster, when crowds of youth — rallied by Morsi’s predominantly liberal and secularist opposition — squared off against police in battles of rocks, molotov cocktails and tear gas in Cairo, Suez and other major cities.

TIMELINE: Key events in Egypt since the fall of Hosni Mubarak.

In Port Said, the serious clashes broke out the following day, after a judge issued death sentences for 21 locals for their involvement in a soccer riot last year. But as Port Said’s death toll rapidly climbed, Egypt’s political opposition, which until last week cut predominantly along religious and class lines, began to broaden.

On Monday the National Salvation Front, a loose coalition of opposition leaders, rejected Morsi’s call to a national dialogue. Leftist leader Hamdeen Sabbahi said the alliance would agree to meet only if Morsi forms a national unity government and begins to amend Egypt’s contentious new constitution, which was approved in a national referendum last month. The front called for more nationwide protests on Friday.

The stakes are high. Egyptian Army Chief Abdel Fatah al-Sissi warned Tuesday of the “collapse of the state” if the crisis continues.

“The continuation of this struggle between the different political forces and their disagreements around the administration of the country could lead to the collapse of the state, and threatens the future of coming generations,” al-Sissi told military academy cadets, according to remarks posted on the armed forces’ Facebook page.

A grim cycle

Morsi’s government and his backers in the Muslim Brotherhood have struggled to control the security crisis. Morsi declared a 30-day state of emergency and a nighttime curfew for Port Said, Suez and Ismailia on Sunday, a day after deploying troops to Port Said and Suez.

But many Egyptians in the emergency zone, spread along Egypt’s most crucial holding, the Suez Canal, said the moves only made them angrier. Thousands took to the streets of Port Said on Monday, beneath the whipping noise of circling helicopters, to bury their dead and defy the curfew.

Some set fire to tires, as one angry protester explained, “to stop the police from attacking.” Men and women carried pictures of young male relatives whom they said had been killed in the two days prior. “The people want the execution of the president,” the crowd chanted.

“We didn’t do what we did because of the 2013 anniversary. We did what we did because of the ruling,” said Mohamed Wahba, the deputy head of the city’s main cemetery. But Wahba, who buried seven people on Monday and 36 the day before, said the grim cycle of protest and death has turned a city that was never overwhelmingly in the Islamists’ favor now decidedly against them.

“The people who come here leave very upset and frustrated, and determined to reject any decision taken by Mohamed Morsi,” he said.

Across a shuttered city, soldiers stood guard outside government and police buildings, including the provincial headquarters and the port. But their presence did little to calm the city’s residents.

Rumors of police snipers and government conspiracy theories swirled through an agitated crowd. And by late afternoon, clashes flared again outside a city police station, amid flying stones and the sporadic sounds of gunfire.

More dissent

In Cairo, protesters clashed sporadically with police on the fringes of Tahrir Square, near the country’s parliament, and across two major downtown thoroughfares, temporarily shutting down a bridge. One man died of a bullet wound, news agencies reported.

In Ismailia, protesters attacked a police station, injuring two police officers with shotgun pellets, local media reported.

The U.S. Embassy in Cairo, which is near Tahrir Square, closed to the public on Monday in anticipation of the protests, State Department spokeswoman Victoria Nuland said. Canada and Britain also closed their embassies.

The seeming permanence of Mubarak’s judiciary and what critics call his abusive police force have fueled much of the anger from Cairo to Port Said, where protesters say their dissent has grown more forceful since Friday, when black-clad riot police used force against them.

The people of Port Said are angry about the way justice played out. The death sentences were politically motivated, residents reasoned, to appease the potentially violent fans of the rival al-Ahly soccer team in Cairo, which claimed most of the 74 riot victims as their own.

“The people are now ignited against anything that represents authority,” said Gharib al-Shalaqany, a retired police lieutenant.

“There is nothing that will calm the people down because they have made Port Said a scapegoat,” said Hisham Mohamed, a government bureaucrat. Last summer, he said, he voted for Morsi. Now: “I wish I could cut my hand off.”

Sharaf al-Hourani in Port Said and Anne Gearan in Washington contributed to this report.