Supporters of Egyptian President Mohamed Morsi clashed with opposition protesters outside the presidential palace Wednesday in the fiercest violence of the country’s two-week-old political crisis, pelting each other with stones and molotov cocktails and intensifying the pressure on Egypt’s embattled new government.

Three of Morsi’s advisers resigned Wednesday evening over the conflict, which has pitted Egypt’s first democratically elected president and his Islamist backers against a broad coalition of liberals, secularists, human rights activists and loyalists to the old regime. Analysts and protesters said the deepening crisis could soon provoke intervention by the country’s military.

Each side accused the other of stoking the violence outside the palace, which health officials said left more than 120 people injured. At least five have been killed in the unrest, Egyptian state television said.

Clashes also broke out Wednesday night near the Cairo headquarters of the Muslim Brotherhood, which is closely allied with Morsi, and in several other major northern cities. Prime Minister Hesham Kandil called on both sides to restore calm.

The opposition is demanding that Morsi rescind a Nov. 22 decree that granted him sweeping powers to legislate without oversight and that he abandon a contentious draft constitution that he has pushed toward a national referendum next week. A disparate group of opposition leaders vowed Wednesday to widen their protest until Morsi backs down.

But Vice President Mahmoud Mekki said the protesters would not derail the referendum. “No political faction can think that they alone monopolize the opinion and have the majority,” he said at a Wednesday news conference. “The judge is the ballot box.”

The United States has refused to criticize Morsi publicly since the crisis began. But U.S. officials said Wednesday that they are working behind the scenes to persuade his government to meet with opposition forces to discuss the draft constitution, which critics say does not protect the rights of women, minorities or the press.

“We call on all stakeholders in Egypt to settle their differences through democratic dialogue, and we call on Egypt’s leaders to ensure that the outcome protects the democratic promise of the revolution for all of Egypt’s citizens,” Secretary of State Hillary Rodham Clinton said Wednesday.

Pressure on the military

But the more violent the situation becomes, and the more divided the country, the more the pressure will grow on the military — which currently enjoys a good relationship with Morsi — to take sides, said Robert Springborg, an expert on the Egyptian military at the Naval Postgraduate School in Monterey, Calif.

The army has traditionally enjoyed wide popular support in Egyptian society and, for a time, was seen as siding with protesters during the revolution that brought down Hosni Mubarak in 2011. But that support faded during a tumultuous 18-month transition period, when Egypt’s top generals ran the country and were accused by rights groups of using violence to quell protests and sending thousands of civilians before military tribunals.

At the moment, Springborg said, the military and Morsi have cemented their relationship through the draft constitution. The document enshrines the military’s autonomy to a degree that surpasses even the Mubarak days, a position the generals might be reluctant to relinquish to secular forces interested in rewriting the charter. But the more they believe that Morsi is mishandling the transition, the more incentive they may have to abandon him, Springborg said, a possibility that may also put pressure on the president to try to settle the crisis.

In some sense, Springborg said, “both sides are looking to the military to decide the future of the country where they are unable as civilians to work it out between themselves.”

The National Association for Change, a liberal activist group in Egypt, issued a statement Wednesday morning that called on the army to stand by protesters in pushing their demands.

‘My street is all rocks now’

Witnesses in the upscale neighborhood of Heliopolis described scenes of shifting “front lines,” flying stones and flames outside the palace Wednesday night, the chaos punctuated by the periodic crack of tear gas canisters from the riot police.

“My street is all rocks now. Every single car on my street has shattered windows,” said Sarah Wali, a business-development manager who watched the clashes from her balcony.

“The scary part is that a lot of this seems to be anger, and it doesn’t seem to have a point,” she said. “I don’t know how a president is sitting, not making announcements and not trying to calm things down.”

Morsi left the presidential palace Tuesday night amid protests outside. But a palace official, who spoke on the condition of anonymity, said the president and his staff had returned to work on Wednesday.

“Egyptians will gather everywhere and use all viable means, and we will not end this battle we entered for freedom and dignity until we are victorious,” said Mohamed ElBaradei, a former head of the International Atomic Energy Agency and a leader of an opposition coalition calling itself the National Salvation Front.

Springborg, the professor, called the crisis a significant moment for the Muslim Brotherhood, which, he said, appears to be splitting over how to respond. Some within the administration see the protests as a chance to beat the opposition into submission, he said, while others, including Morsi, are advocating restraint.

Members of the opposition said they have yet to agree on how to proceed if the protests do not halt the government’s march toward a referendum.

Much of the country’s judiciary has come out against Morsi’s decree. But the Supreme Judicial Council said Monday that it would oversee the referendum as a way out of the political crisis, offering the possibility of legal credibility for the vote.

Ingy Hassieb in Cairo and Anne Gearan in Brussels contributed to this report.